Refactor BLS module

[samlaf]

We originally took much of the crypto/bls module from eigenDA, so it currently contains code for both bls and some incredible-squaring specific code.

We need to refactor it and take out all the incredible-squaring code and put that in its own repo.

[samlaf]

I really don't like that our bn254 and bls methods all take pointer receivers and arguments, eg:

func (p *G2Point) Add(p2 *G2Point)

I've been bitten a few times by side effects while writing the bls aggregation service. I think we just followed the gnark-crypto library design. I raised an issue in their repo asking for the rationale behind this design choice. In the meantime, I think we might want to switch to non pointer receivers and args. A few stack copies is not worth optimizing for, especially if it can save a bunch of human debugging time.

EDIT: I'm stupid, you're smart. I was wrong, you are right. Actually I now don't like our interface for a different set of reasons, listed in that issue. Feels like we should just use the underlying bn254 methods directly (that take receiver and 2 pointer arguments)!

[samlaf]

gnark-crypto has a PR open to add bls sigs over a bunch of curves. We should consider using their implementation once they merge it. It's been open and stale for quite a while though...