* feat: change bytecode hash function from Keccak to Poseidon
* fix TestStateProcessorErrors
* rename files
* copy iden3's poseidon package to local
* update poseidon hash
* apply new hash in codehash
* extend hash method, use actual code size as cap
* prune keccak(nil) for empty code
* update empty code hash references to Poseidon
* add TestPoseidonCodeHash
* use keccak for empty code hash
* go mod tidy
* goimports
* use Poseidon code hash in state and sync tests
* run goimports
* run goimports
* remove unnecessary reallocation from CodeHash
* goimports
* move codehash API to separate module
* add missing package
* fix review comments
* improve comments
Co-authored-by: Ho Vei <noelwei@gmail.com>
