CIP-31 - BLS12-381 Precompiles

[kilic]

Description

This PR adds BLS12-381 elliptic curve precompiles as defined in EIP-2537.

Other changes

• added BLS12-381 elliptic curve library added to ./crypto/bls12381
• added precompile runners with addresses and gas schedule.
• created new set of precompiles named PrecompiledContractsDonut
• added test vectors generated with https://github.com/matter-labs/eip1962

Tested

Underlying elliptic curve library is heavily tested in terms of mathematical properties.

Original library BLS12-381 is subjected to the security audit under drand project and also made its way to be backend of EIP-2537 go-ethereum precompiles.

[prestwich]

hey @kilic, I'm starting to shephard client integration. :) Can you please do the following:

1. once tests: change precompile tests to use Donut block #1286 is merged, rebase onto latest master
2. Remove your current address declarations
3. Remove any activation logic (including any rows in the istanbul precompile block)
4. Fill in the rows in the Donut Precompile block

[trianglesphere]

First pass, generally looks good, but do remember to charge gas. This also applies to the PR for BLS12-377

[trianglesphere]

FYI the first step of any pre-compile function should be to debit the gas
Example code:

	gas, err := debitRequiredGas(c, input, gas)
	if err != nil {
		return nil, gas, err
	}

[mcortesi]

Closed in favor of #1340