Field generator macros

[kilic]

This PR adds field generator macros and as a result removes many duplicates. There is an important breaking change that it now wraps all field representations for example as ReprFq([u8; SIZE]).

Also it will help to add new fields and thus new curves. For example base field for BLS12-381 which has 6 limbs internal representation can be added as:

impl_field!(
    bls12381_scalar,
    Fp,
    modulus = "1a0111ea397fe69a4b1ba7b6434bacd764774b84f38512bf6730d2a0f6b0f6241eabfffeb153ffffb9feffffffffaaab",
    mul_gen = "2",
    zeta = "1a0111ea397fe699ec02408663d4de85aa0d857d89759ad4897d29650fb85f9b409427eb4f49fffd8bfd00000000aaac",
    from_uniform = [96],
);

[davidnevadoc]

Finished first pass and left some comments.
Looking amazing so far :)

[davidnevadoc]

LGTM! Good job 🎉
Left some minor comments, but I think this can be merged.
Since it is such a big change, I wouldn't mind having an extra review though.

[han0110]

LGTM! Nice rework! Just left some small suggestions.