test vectors

[turuslan]

• spec test vectors: fork choice, state transition, ssz, verify signatures
  • blocks json field didn't use camelCase leanEthereum/leanSpec#157
  • proposer attestation and checks hashes leanEthereum/leanSpec#184
• fix regression in updateHead() after Refactor: block tree and fork choice #51, latest new/known attestations
• dontPropose() to disable proposing/voting in tests
• merge ssz and json macro SSZ_AND_JSON_FIELDS
• json camel (test vectors) and snake (api) case
• fixtures
• disabled tests
  • ssz PublicKey xmss internal format
  • json contains invalid proposer attestation in last block, target < source
    • test_fork_choice_reorgs.py::test_reorg_on_newly_justified_slot
    • test_signature_aggregation.py::test_all_validators_attest_in_single_aggregation
    • test_signature_aggregation.py::test_multiple_specs_same_target_merge_into_one
    • test_finalization_mid_processing.py::test_finalization_advances_mid_attestation_processing