Standardize on terminology: coset_shifts vs coset_gens

[kevaundray]

This has been taken from Benedikt Wagner's document.

We use coset_shifts and coset_gens interchangeably to mean the same thing.

Link:

rust-eth-kzg/cryptography/kzg_multi_open/src/fk20/verifier.rs

Line 58 in e043452

let coset_shifts = coset_gens(num_points_to_open, num_cosets, BIT_REVERSED);

Related to #246

[b-wagn]

No strong opinion on which of them is better. Maybe check the spec: it uses shifts here. So maybe go with shifts?

[kevaundray]

closed by #281

[kevaundray]

Noted in the PR, I went with coset_gens short for coset_generators since I didn't think coset_shifts is well-defined; they are just generators for a coset. It might make sense to change it in the specs but no hard opinion