* add Altair fork tests for upgrade_to_altair() * Deposit processing ensures all keys are valid
* fix Altair epoch state transitions * re-enable and re-add near-complete Altair epoch processing test vectors: inactivity, justification & finalization, participation flag, slashings, and sync committee updates
* bump nim-eth2-vendors and use v1.1.0-alpha6 test vectors * continue to download alpha 5 test vectors for const sanity checks
* reorganize SSZ-based tests to support phase0 and altair * label Altair SSZ consensus object tests as such * update test summary