fix(consensus,XDPoS/v2): do not reject syncInfo when the sender has no TC yet

[wanwiset25]

Proposed changes

TC only exists in memory. When a node fresh restarts, there is no real TC, only the initial blank. Round 0 with no signatures is the bootstrap TC installed by New(), not a real certificate: a TC only comes into existence once a round has timed out. Rejecting it would discard the whole syncInfo, which might have a useful QC.

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• test: Adding missing tests or correcting existing tests

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• Consensus
• Account
• Network
• Geth
• Smart Contract
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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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[Copilot]

Pull request overview

Allows valid SyncInfo QCs to be processed when accompanied by the initial blank timeout certificate.

Changes:

• Detects bootstrap TCs.
• Skips TC verification only for blank round-zero certificates.
• Adds positive and boundary tests.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
consensus/XDPoS/engines/engine_v2/timeout.go	Adds blank-TC detection.
consensus/XDPoS/engines/engine_v2/engine.go	Exempts blank TCs during SyncInfo verification.
consensus/tests/engine_v2_tests/sync_info_test.go	Tests bootstrap and non-empty TC behavior.

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