Refactor: remove geth dependency

[yelhousni]

Use gnark-crypto instead of geth/crypto for secp256k1 and ecdsa.
This needs Consensys/gnark-crypto#310 to be merged first.

[yelhousni]

needs to be updated after Consensys/gnark-crypto#313 and Consensys/gnark-crypto#314 get merged in gnark-cypto.

[ivokub]

So, right now there is a slight problem - when we sign with gnark-crypto, as a signature we get a []byte, but it is difficult to get R and S from the signature. We would have to instantiate fr-specific ecdsa.Signature, unmarshal it from bytes and assign from it. It involves a type-switch, but I think it is ok.

I have some ideas and will try to push the changes.

[ivokub]

Rebased on top of develop, added a few more changes (avoid explicit conversion to *big.Int, rename package import, update go.mod).

Previously I totally overthought it. I think the simple approach is better (read signature directly into secp256k1 ECDSA signature struct and get R and S from there).

As far as it seems then the failing tests are due to MiMC hashing. Imo are unrelated to this PR.