Simplify logic of from(unsigned)

[z-tech]

What does this PR do?

• calls from(u128) in functions: from(u8), from(u16), from(u32), from(u64)
• performs reduction in from(u128) needed to match behavior of BigInt impl

    let test0 = M31::from(9991293939349493_u128);
    let test1 = SmallM31::from(9991293939349493_u128);
    println!("test0: {}", test0);
    println!("test1: {}", test1);
    
    output:
    test0: 1717630467
    test1: 1717630467