make consensus app generic over `ExecutionLayer`

[rnbguy]

the main refactoring PR. replace every engine: &Engine parameter in app/src/ with el: &E where E: ExecutionLayer. move app logic into crates/consensus/malachite/.

what moves + changes

source	destination	change
app/src/app.rs	consensus/malachite/src/app.rs	engine: &Engine -> el: &E in all handlers
app/src/state.rs	consensus/malachite/src/state.rs	remove eth_chain_config, get_fork(), ValidatedPayloadCache
app/src/bootstrap.rs	consensus/malachite/src/bootstrap.rs	use trait methods
app/src/sync_handler.rs	consensus/malachite/src/sync_handler.rs	el.get_block_by_height() + el.encode_block()
app/src/store.rs	consensus/malachite/src/store.rs	unchanged
app/src/streaming.rs	consensus/malachite/src/streaming.rs	unchanged
app/src/node.rs	consensus/malachite/src/node.rs	App<E>, Engine construction moves to CLI
app/src/metrics.rs	consensus/malachite/src/metrics.rs	unchanged

handler-level changes

handler	before	after
on_consensus_ready	engine.check_capabilities(), engine.eth.get_block_by_number("earliest")	el.genesis_block()
on_get_value	engine.is_syncing(), engine.generate_block(...)	el.is_syncing(), el.build_block(parent, ts)
on_decided	engine.set_latest_forkchoice_state(hash, retry), read_validators_from_contract(url, hash)	el.finalize_block(&block) -> BlockId, el.validator_set()
on_process_synced_value	validate_execution_payload(cache, data, h, r, engine, retry)	el.validate_block(&block)
on_get_decided_value	get_decided_value_for_sync(store, engine, h, earliest)	get_decided_value_for_sync(store, el, h, earliest)
on_started_round	state.process_complete_proposal_parts(parts, engine, &config.retry_config)	state.process_complete_proposal_parts(parts, el)