* fix remaining block pool extended validation issues and re-enable first-block-received and block-signature EV checks; enable Merkle validation in beacon_node in eth2_network_simulation; refactor some Merkle proof generation code outside tests/ as a result
* re-enable Merkle validation skipping, since while it works on make eth2_network_simulation, it has issues with local testnet
* tighten already-seen-block blockpool check; move comment closer to conceptually proximate code; queue up maybe-future-valid-blocks as pending to keep libp2p-synchronous interrupt handling time lower
* revert the cleanups, now in a separate PR
* remove the remaining merkle_minimal cleanup remnants, also moved to other PR
* restore PR to only modifying one file after rebasing
* use signatures as summary to compare block contents
* switch signature comparison to be raw byte-wise to ensure no attempts to deserialize it to valid (or not) BLS signatures first
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