Add Fixed-Size Unsigned Integer Interface to ECLAIR

[bhgomes]

For a given number of bits (less than 1/2 the proof-system field size), we should have an interface for operations that need to have bounds checking enabled. Build a new type that's something like the following:

/// 128-Bit Unsigned Integer
pub struct U128<T>(T);

impl<T> U128<T> {
    /// Builds a new [`U128`] over `value`, asserting that it does not exceed 128 bits.
    #[inline]
    pub fn new<COM>(value: T, compiler: &mut COM) -> Self 
    where
        COM: AssertWithinRange<T, 128>,
    {
        compiler.assert_within_range(value);
        Self(value)
    }
}

where the following trait implementations have a range check included for each operation:

• Add<Self, COM>
• AddAssign<COM>
• Sub<Self, COM>
• SubAssign<COM>

We can leave the multiplicative operations for the future (not needed for the next version of protocol). Once this interface is built out, we can expand to all integral types less than 128.