fix failing doc test and clear up docs

# Objective

Alternative to bevyengine#6150

Dependabot's PR doesn't seem to break anything, but there are some deprecations that we might as well fix up.

## Solution

https://github.com/clap-rs/clap/blob/master/CHANGELOG.md#migrating

Update clap in `build-wasm-example` and `span-cmp`. Other tools don't use clap.

Remove references to `value_parser`. It's the default now.

Change `#[clap()]` to `#[arg()]`.

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

crates/bevy_tasks/src/task_pool.rs

@@ -164,11 +164,19 @@ impl TaskPool {
     ///     });
     /// });
     ///
-    /// // results are returned in the order the tasks are spawned in.
-    /// // Note: the ordering may become non-deterministic if you spawn from within tasks.
-    /// // the ordering is only guaranteed when tasks are spawned directly from the main closure.
+    /// // The ordering of results is non-deterministic if you spawn from within tasks as above.
+    /// // This commented out assert will fail intermittently because the inner spawn can be inserted into
+    /// // the queue before the outer one.
+    /// // assert_eq!(&results[..], &[0, 1]);
+    ///
+    /// // The ordering is deterministic if you only spawn directly from the closure function.
+    /// let results = pool.scope(|s| {
+    ///     s.spawn(async { 0  });
+    ///     s.spawn(async { 1 });
+    /// });
     /// assert_eq!(&results[..], &[0, 1]);
-    /// // can access x after scope runs
+    ///
+    /// // You can access x after scope runs, since it was only temporarily borrowed in the scope.
     /// assert_eq!(x, 2);
     /// ```
     ///