chore: document array methods (#6034)

# Description

## Problem

Part of #5797

## Summary



## Additional Context



## Documentation

Check one:
- [ ] No documentation needed.
- [x] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

docs/docs/noir/concepts/data_types/arrays.md

@@ -251,7 +251,6 @@ fn main() {
     let any = arr.any(|a| a == 5);
     assert(any);
 }
-
 ```
 
 ### as_str_unchecked

noir_stdlib/src/array/mod.nr

@@ -6,15 +6,42 @@ mod check_shuffle;
 mod quicksort;
 
 impl<T, let N: u32> [T; N] {
-    /// Returns the length of the slice.
+    /// Returns the length of this array.
+    /// 
+    /// ```noir
+    /// fn len(self) -> Field
+    /// ```
+    /// 
+    /// example
+    /// 
+    /// ```noir
+    /// fn main() {
+    ///     let array = [42, 42];
+    ///     assert(array.len() == 2);
+    /// }
+    /// ```
     #[builtin(array_len)]
     pub fn len(self) -> u32 {}
 
+    /// Returns this array as a slice.
+    /// 
+    /// ```noir
+    /// let array = [1, 2];
+    /// let slice = array.as_slice();
+    /// assert_eq(slice, &[1, 2]);
+    /// ```
     #[builtin(as_slice)]
     pub fn as_slice(self) -> [T] {}
 
-    // Apply a function to each element of an array, returning a new array
-    // containing the mapped elements.
+    /// Applies a function to each element of this array, returning a new array containing the mapped elements.
+    /// 
+    /// Example:
+    /// 
+    /// ```rust
+    /// let a = [1, 2, 3];
+    /// let b = a.map(|a| a * 2);
+    /// assert_eq(b, [2, 4, 6]);
+    /// ```
     pub fn map<U, Env>(self, f: fn[Env](T) -> U) -> [U; N] {
         let first_elem = f(self[0]);
         let mut ret = [first_elem; N];
@@ -26,19 +53,42 @@ impl<T, let N: u32> [T; N] {
         ret
     }
 
-    // Apply a function to each element of the array and an accumulator value,
-    // returning the final accumulated value. This function is also sometimes
-    // called `foldl`, `fold_left`, `reduce`, or `inject`.
+    /// Applies a function to each element of the array, returning the final accumulated value. The first
+    /// parameter is the initial value.
+    /// 
+    /// This is a left fold, so the given function will be applied to the accumulator and first element of
+    /// the array, then the second, and so on. For a given call the expected result would be equivalent to:
+    /// 
+    /// ```rust
+    /// let a1 = [1];
+    /// let a2 = [1, 2];
+    /// let a3 = [1, 2, 3];
+    /// 
+    /// let f = |a, b| a - b;
+    /// a1.fold(10, f); //=> f(10, 1)
+    /// a2.fold(10, f); //=> f(f(10, 1), 2)
+    /// a3.fold(10, f); //=> f(f(f(10, 1), 2), 3)
+    /// 
+    /// assert_eq(a3.fold(10, f), 10 - 1 - 2 - 3);
+    /// ```
     pub fn fold<U, Env>(self, mut accumulator: U, f: fn[Env](U, T) -> U) -> U {
         for elem in self {
             accumulator = f(accumulator, elem);
         }
         accumulator
     }
 
-    // Apply a function to each element of the array and an accumulator value,
-    // returning the final accumulated value. Unlike fold, reduce uses the first
-    // element of the given array as its starting accumulator value.
+    /// Same as fold, but uses the first element as the starting element.
+    /// 
+    /// Example:
+    /// 
+    /// ```noir
+    /// fn main() {
+    ///     let arr = [1, 2, 3, 4];
+    ///     let reduced = arr.reduce(|a, b| a + b);
+    ///     assert(reduced == 10);
+    /// }
+    /// ```
     pub fn reduce<Env>(self, f: fn[Env](T, T) -> T) -> T {
         let mut accumulator = self[0];
         for i in 1..self.len() {
@@ -47,7 +97,17 @@ impl<T, let N: u32> [T; N] {
         accumulator
     }
 
-    // Returns true if all elements in the array satisfy the predicate
+    /// Returns true if all the elements in this array satisfy the given predicate.
+    /// 
+    /// Example:
+    /// 
+    /// ```noir
+    /// fn main() {
+    ///     let arr = [2, 2, 2, 2, 2];
+    ///     let all = arr.all(|a| a == 2);
+    ///     assert(all);
+    /// }
+    /// ```
     pub fn all<Env>(self, predicate: fn[Env](T) -> bool) -> bool {
         let mut ret = true;
         for elem in self {
@@ -56,7 +116,17 @@ impl<T, let N: u32> [T; N] {
         ret
     }
 
-    // Returns true if any element in the array satisfies the predicate
+    /// Returns true if any of the elements in this array satisfy the given predicate.
+    /// 
+    /// Example:
+    /// 
+    /// ```noir
+    /// fn main() {
+    ///     let arr = [2, 2, 2, 2, 5];
+    ///     let any = arr.any(|a| a == 5);
+    ///     assert(any);
+    /// }
+    /// ```
     pub fn any<Env>(self, predicate: fn[Env](T) -> bool) -> bool {
         let mut ret = false;
         for elem in self {
@@ -67,17 +137,44 @@ impl<T, let N: u32> [T; N] {
 }
 
 impl<T, let N: u32> [T; N] where T: Ord + Eq {
+    /// Returns a new sorted array. The original array remains untouched. Notice that this function will
+    /// only work for arrays of fields or integers, not for any arbitrary type. This is because the sorting
+    /// logic it uses internally is optimized specifically for these values. If you need a sort function to
+    /// sort any type, you should use the `sort_via` function.
+    /// 
+    /// Example:
+    /// 
+    /// ```rust
+    /// fn main() {
+    ///     let arr = [42, 32];
+    ///     let sorted = arr.sort();
+    ///     assert(sorted == [32, 42]);
+    /// }
+    /// ```
     pub fn sort(self) -> Self {
         self.sort_via(|a: T, b: T| a <= b)
     }
 }
 
 impl<T, let N: u32> [T; N] where T: Eq {
-
-    /// Sorts the array using a custom predicate function `ordering`.
-    ///
-    /// The `ordering` function must be designed to return `true` for equal valued inputs
-    /// If this is not done, `sort_via` will fail to sort inputs with duplicated elements.
+    /// Returns a new sorted array by sorting it with a custom comparison function. 
+    /// The original array remains untouched. 
+    /// The ordering function must return true if the first argument should be sorted to be before the second argument or is equal to the second argument.
+    /// 
+    /// Using this method with an operator like `<` that does not return `true` for equal values will result in an assertion failure for arrays with equal elements.
+    /// 
+    /// Example:
+    /// 
+    /// ```rust
+    /// fn main() {
+    ///     let arr = [42, 32]
+    ///     let sorted_ascending = arr.sort_via(|a, b| a <= b);
+    ///     assert(sorted_ascending == [32, 42]); // verifies
+    /// 
+    ///     let sorted_descending = arr.sort_via(|a, b| a >= b);
+    ///     assert(sorted_descending == [32, 42]); // does not verify
+    /// }
+    /// ```
     pub fn sort_via<Env>(self, ordering: fn[Env](T, T) -> bool) -> Self {
         unsafe {
             // Safety: `sorted` array is checked to be:
@@ -99,13 +196,23 @@ impl<T, let N: u32> [T; N] where T: Eq {
 }
 
 impl<let N: u32> [u8; N] {
-    /// Convert a sequence of bytes as-is into a string.
-    /// This function performs no UTF-8 validation or similar.
+    /// Converts a byte array of type `[u8; N]` to a string. Note that this performs no UTF-8 validation -
+    /// the given array is interpreted as-is as a string.
+    /// 
+    /// Example:
+    /// 
+    /// ```rust
+    /// fn main() {
+    ///     let hi = [104, 105].as_str_unchecked();
+    ///     assert_eq(hi, "hi");
+    /// }
+    /// ```
     #[builtin(array_as_str_unchecked)]
     pub fn as_str_unchecked(self) -> str<N> {}
 }
 
 impl<let N: u32> From<str<N>> for [u8; N] {
+    /// Returns an array of the string bytes.
     fn from(s: str<N>) -> Self {
         s.as_bytes()
     }