feat: BLS signatures over BLS12-381 curve

[nulltea]

Add BLS signatures for newly added BLS12-381. Relies on axiom-crypto/halo2curves#8. It should be merged after #175.

Open questions:

• is there a need for BlsSignatureChip trait to standardize for BN256 and BLS12-381 curves?

Benchmarks

test_bls_signature (verify 1 BLS signature w/o hash to curve) k=19 lookup_bits=18:

Gate Chip | Phase 0: 4960683 advice cells
Total 82 fixed cells
Total range check advice cells to lookup per phase: [619032, 0, 0]