Mini-Epic: Stop tokio tasks running for a long time and blocking other tasks

[teor2345]

Motivation

At the moment, Zebra can't sync all the way to the tip, because some tokio tasks run for a long time, and block other tasks.
(It's also possible there are some deadlocks, livelocks, or missed task exits.)

We should discover the specific bugs using tokio-console, and then open a ticket for each one.

Tasks

Issues that need investigation

• Investigate busiest tasks per tokio-console #4583
• Find out which parts of CommitBlock/CommitFinalizedBlock are slow #4823 and then speed them up
• Add a Future wrapper that times each poll, and logs long polls

CPU usage analysis

• 1. fix(state): Stop reading redundant blocks for every FindHashes and FindHeaders request #4825 & 2. fix(state): Make FindHeaders and FindHashes run concurrently with state updates #4826

• Move zebra-state writes to blocking threads #4779

Deserialization (in zebra-network or zebra-state):

• sapling::output::OutputPrefixInTransactionV5::zcash_deserialize() (Move network transaction deserialization to a dedicated blocking and CPU-heavy thread #4787)
  • sapling::committment::ValueCommitment::try_from::<[u8; 32]>()
  • bellman::groth16::Proof::read()
  • jubjub::AffinePoint::from_bytes_inner()
  • bls12_381::scalar::square()
  • bls12_381::scalar::sqrt()
• finalized_state::ZebraDb::block() (Move database block and transaction fetches to a dedicated blocking and CPU-heavy thread #4788)
  • partially fixed by 1. fix(state): when sending headers to peers, only deserialize the header data from disk #4792

Verification (in zebra-consensus):

• groth16::DescriptionWrapper::try_from() (Move CPU-heavy proof preparation into the batch cryptography thread #4789)
  • transaction::Verifier::verify_v5_transaction()

Note commitment tree updates (in zebra-state, either finalized or non-finalized):

• Note commitment tree append and root (Move note commitment tree updates to a dedicated blocking and CPU-heavy thread #4790)
  • non_finalized_state::chain::UpdateWith
  • sapling::tree::merkle_crh_sapling()
  • sapling::commitment::pedersen_hashes::pedersen_hash()
  • sapling::commitment::pedersen_hashes::pedersen_hash_to_point()
  • incrementalmerkletree::bridgetree::Frontier::append()
• feat(state): Send treestate from non-finalized state to finalized state #4721 should also help with non-finalized blocks

Fixed Issues

• Investigate "tasks have lost their waker" and fix if needed #4581

Fixed by #4750:

• Check for Worker panics in tower_batch::Batch #4738
• Run groth16, ed25519, and redjubjub batches on a blocking thread #4740
• Stop batch verification lagging and failing entire batches #4729
• Replace batch verifier broadcast channels with watch channels (cleanup only)

Fixed by #4752 and #4726:

• Zebra is slow near the tip #4650
• Lagged inventory advertisements (might also need fix(batch): Improve batch verifier async, correctness, and performance #4750)
• Verification failure after block 1719629 on mainnet (also block 1944652 on testnet is very slow)

[teor2345]

We've made enough performance improvements for now.