blst lagrange interpolation

[dknopik]

Proof of concept of using blst for signature recovery.

We should discuss whether we want to use this or blsful.

Arguments for this impl:

• We avoid a bunch of new dependencies (which is nice, as we are working with keys here)
• We do not have to add too much ugly switching of types this way (as blsful uses a whole stack of own types. Lighthouse instead uses their own bls crate that builds upon blst)
• I daresay it's faster, but I have not tested that 😬

Arguments for blsful:

• No unsafe needed
• This impl needs some (hopefully harmless) changes upstreamed to blst
• DIY cryptography is scary

[Zacholme7]

do you have a poc using blsful? Id almost say not having to use unsafe and roll some diy cryptography is worth more messy types but there are valid arguments for both libs.

[dknopik]

@Zacholme7 not yet, will do