fix(eth/bft): avoid broadcast send blocking during shutdown

[gzliudan]

Proposed changes

Guard BFT broadcast enqueue with the quit channel so Vote/Timeout/SyncInfo exit cleanly once shutdown starts.

Add a regression test to ensure Vote returns after BFT loop stop and does not hang.

log messages when stop node without this PR:

INFO [05-21|13:01:19.273] [getTCEpochInfo] Init epochInfo          number=82,155,518 round=25893000   tcRound=25893274 tcEpoch=91913
INFO [05-21|13:01:19.273] [getTCEpochInfo] Final TC epochInfo      number=82,155,518 round=25893000   tcRound=25893274 tcEpoch=91913
INFO [05-21|13:01:19.273] Timeout pool threashold reached: true, number of items in the pool: 22
INFO [05-21|13:01:19.273] [setNewRound] new round and reset pools and workers round=25893275
INFO [05-21|13:01:19.273] [onTimeoutPoolThresholdReached] process TC successfully TcRound=25893274 NumberOfTcSig=22
INFO [05-21|13:01:19.348] [getTCEpochInfo] Init epochInfo          number=82,155,518 round=25893000   tcRound=25893275 tcEpoch=91913
INFO [05-21|13:01:19.349] [getTCEpochInfo] Final TC epochInfo      number=82,155,518 round=25893000   tcRound=25893275 tcEpoch=91913
INFO [05-21|13:01:19.353] Imported new chain segment               blocks=1   txs=0    mgas=0.000  elapsed=1.694ms       mgasps=0.000   number=82,155,770 hash=fa80d0..d8ffca dirty=0.00B
INFO [05-21|13:01:19.469] [voteHandler] Vote pool threashold reached: true, number of items in the pool: 22
INFO [05-21|13:01:19.470] [commitBlocks] Rounds not continuous(parent) found when committing block proposedBlockRound=25893275 decodedExtraField.Round=25893273 proposedBlockHeaderHash=fa80d0..d8ffca
INFO [05-21|13:01:19.470] [setNewRound] new round and reset pools and workers round=25893276
INFO [05-21|13:01:19.470] Successfully processed the vote and produced QC! QcRound=25893275 QcNumOfSig=22 QcHash=fa80d0..d8ffca QcNumber=82,155,770
INFO [05-21|13:01:19.470] [voteHandler] time cost from receive first vote under QC create elapsed=10.23727721s
INFO [05-21|13:01:19.821] Got interrupt, shutting down...
INFO [05-21|13:01:19.828] HTTP server stopped                      endpoint=[::]:8745
INFO [05-21|13:01:19.831] HTTP server stopped                      endpoint=[::]:9745
INFO [05-21|13:01:19.832] IPC endpoint closed                      url=/home/me/xdc_chain/testnet_1/XDC.ipc
INFO [05-21|13:01:19.833] Stopping Ethereum bloomIndexer start
INFO [05-21|13:01:19.833] Ethereum bloomIndexer stopped
INFO [05-21|13:01:19.833] Stopping Ethereum blockchain start
INFO [05-21|13:01:19.833] Blockchain manager stopped
INFO [05-21|13:01:19.833] Ethereum blockchain stopped
INFO [05-21|13:01:19.833] Stopping Ethereum protocolManager start
INFO [05-21|13:01:19.835] Stopping Ethereum protocol
WARN [05-21|13:01:19.839] BFT Loop Close
INFO [05-21|13:01:19.842] Ethereum protocol stopped
INFO [05-21|13:01:19.842] Ethereum protocolManager stopped
INFO [05-21|13:01:19.842] Stopping Ethereum txPool start
INFO [05-21|13:01:19.842] Transaction pool stopped
INFO [05-21|13:01:19.842] Ethereum txPool stopped
INFO [05-21|13:01:19.842] Stopping Ethereum shutdownChan start
INFO [05-21|13:01:19.842] Ethereum shutdownChan stopped
INFO [05-21|13:01:19.842] Stopping Ethereum miner start
INFO [05-21|13:01:19.842] Ethereum miner stopped
INFO [05-21|13:01:19.842] Stopping Ethereum eventMux start
INFO [05-21|13:01:19.842] Ethereum eventMux stopped
INFO [05-21|13:01:19.842] Stopping Ethereum chainDb start
INFO [05-21|13:01:20.308] Ethereum chainDb stopped
WARN [05-21|13:01:27.011] Propagated block verification failed     peer=386884ee0aa5383d number=82,154,346 hash=e14937..07a462 err="unknown ancestor"
WARN [05-21|13:02:43.000] Propagated block verification failed     peer=386884ee0aa5383d number=82,154,376 hash=11895e..23d420 err="unknown ancestor"
WARN [05-21|13:03:59.001] Propagated block verification failed     peer=386884ee0aa5383d number=82,154,406 hash=29cc51..857659 err="unknown ancestor"

Types of changes

What types of changes does your code introduce to XDC network?
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• build: Changes that affect the build system or external dependencies
• ci: Changes to CI configuration files and scripts
• chore: Changes that don't change source code or tests
• docs: Documentation only changes
• feat: A new feature
• fix: A bug fix
• perf: A code change that improves performance
• refactor: A code change that neither fixes a bug nor adds a feature
• revert: Revert something
• style: Changes that do not affect the meaning of the code
• test: Adding missing tests or correcting existing tests

Impacted Components

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• Consensus
• Account
• Network
• Geth
• Smart Contract
• External components
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Checklist

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• This PR has sufficient test coverage (unit/integration test) OR I have provided reason in the PR description for not having test coverage
• Tested on a private network from the genesis block and monitored the chain operating correctly for multiple epochs.
• Provide an end-to-end test plan in the PR description on how to manually test it on the devnet/testnet.
• Tested the backwards compatibility.
• Tested with XDC nodes running this version co-exist with those running the previous version.
• Relevant documentation has been updated as part of this PR
• N/A

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