* restore EpochRef and flush statecaches on epoch transitions
* more targeted cache invalidation
* remove get_empty_per_epoch_cache(); implement simpler but still faster get_beacon_proposer_index()/compute_proposer_index() approach; add some abstraction layer for accessing the shuffled validator indices cache
* reduce integer type conversions
* remove most of rest of integer type conversion in compute_proposer_index()
* fix some warnings related to beacon_node splitting; reimplement finalization verification more robustly; improve attestation pool block selection logic
* re-add missing import
* whitelist allowed state transition flags and make rollback/restore naming more consistent
* restore usage of update flags passed into skipAndUpdateState(...) in addition to the potential verifyFinalization flag
* switch rest of rollback -> restore
* remove near-duplicate code paths: process_slot(), process_slots(), and state_transition() for BeaconState are now wrappers around the HashedBeaconState versions
* convert tests/test_state_transition.nim to use HashedBeaconState
* convert mocking infrastructure and spec_block/epoch_processing tests to use HashedBeaconBlock, and remove thus unused process_slot*(state: var BeaconState)
* rename compute_epoch_of_slot(...) to compute_epoch_at_slot(...)
* remove some unnecessary imports; remove some crosslink-related code and tests; complete renaming of compute_epoch_of_slot(...) to compute_epoch_at_slot(...)
* rm more transfer-related code and tests; rm more unnecessary strutils imports
* rm remaining unused imports
* remove useless get_empty_per_epoch_cache(...)/compute_start_slot_of_epoch(...) calls
* rename compute_start_slot_of_epoch(...) to compute_start_slot_at_epoch(...)
* rename ACTIVATION_EXIT_DELAY to MAX_SEED_LOOKAHEAD
* update domain types to 0.9.0
* mark AttesterSlashing, IndexedAttestation, AttestationDataAndCustodyBit, DepositData, BeaconBlockHeader, Fork, integer_squareroot(...), and process_voluntary_exit(...) as 0.9.0
* mark increase_balance(...), decrease_balance(...), get_block_root(...), CheckPoint, Deposit, PendingAttestation, HistoricalBatch, is_active_validator(...), and is_slashable_attestation_data(...) as 0.9.0
* mark compute_activation_exit_epoch(...), bls_verify(...), Validator, get_active_validator_indices(...), get_current_epoch(...), get_total_active_balance(...), and get_previous_epoch(...) as 0.9.0
* mark get_block_root_at_slot(...), ProposerSlashing, get_domain(...), VoluntaryExit, mainnet preset Gwei values, minimal preset max operations, process_block_header(...), and is_slashable_validator(...) as 0.9.0
* mark makeWithdrawalCredentials(...), get_validator_churn_limit(...), get_total_balance(...), is_valid_indexed_attestation(...), bls_aggregate_pubkeys(...), initial genesis value/constants, Attestation, get_randao_mix(...), mainnet preset max operations per block constants, minimal preset Gwei values and time parameters, process_eth1_data(...), get_shuffled_seq(...), compute_committee(...), and process_slots(...) as 0.9.0; partially update get_indexed_attestation(...) to 0.9.0 by removing crosslink refs and associated tests
* mark initiate_validator_exit(...), process_registry_updates(...), BeaconBlock, Eth1Data, compute_domain(...), process_randao(...), process_attester_slashing(...), get_base_reward(...), and process_slot(...) as 0.9.0
* Introduce new mocking proc to replace:
- makeFakeValidatorPrivKey
- hackPrivKey
- getNextBeaconProposerIndex
- addBlock
- makeBlock
* Add comments on datastructure unsynced with the spec
* Add merkle tree constructor and initial mocking for deposits (missing merkle proofs)
* [Mock] Implement sparse merkle tree and merkle proof builder
* [Mocking] Genesis deposits
* Add compact_committees_roots init + mock genesis state
* [Tests] Add first deposit test using the new mocking procedures
* [Tests -deposits] add at and over 32 ETH deposit tests
* [Tests - deposits] Add test for validator top-up
* [Tests -deposits] Mention the TODO to test for invalid conditions
* [Tests] Add stub to test "is_valid_genesis_state"
* [Merkle proofs] Implement round-trip checks
* Deactivate roundtrips test
* SSZ - use EF convention for hash_tree_root / hashTreeRoot
* [Tests - Attestation] Attestation mocking + initial test
* Add mocking + 3 new tests for valid attestations + mention future invalid attestation tests
* Add crosslinks test (1 failing to attestations in block being duplicated in state transition)
* Single attestation crosslink test - workaround https://github.com/status-im/nim-beacon-chain/issues/361
* Add test for failed crosslink penalty
* Rebase fixes + add refactored tests to test suite
* justif-finalization helpers first batch
* Add 234 finalization tests
* Fix justif test, Rule I 234 finalization does not happen with sufficient support.
(Also unittest check template does not fail properly in some cases)
* Add tests for all finalization rules
* Properly delete nim-byteutils following c91727e7e5 (diff-7c3613dba5171cb6027c67835dd3b9d4)
* use digest helper for deposit root