statesync: record finalized version only after state root validation

[kkuehlz]

monad_statesync_client_finalize previously marked the target finalized before comparing the canonical trie's state root against the trusted header. A peer supplying syntactically valid but corrupted state thus became the client's restart baseline: reopening rewinds to the recorded finalized version and initializes sync progress from it, so a normal retry never re-requested the corrupted range. Validate the root first and only then update the finalized version, and warn when a target is rejected.

[Copilot]

Pull request overview

This PR fixes a statesync correctness issue where monad_statesync_client_finalize could persist a corrupted sync target as the client’s restart baseline by updating the finalized version before validating the canonical trie’s state root against the trusted header.

Changes:

• Delay update_finalized_version(tgrt.number) until after state_root() matches the trusted target header.
• Emit a warning when the target is rejected due to a root mismatch.
• Add a regression test to ensure restart-after-failure does not inherit the corrupted baseline.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
category/statesync/statesync_client.cpp	Reorders finalize to validate state root before persisting finalized version; adds warning log on mismatch.
category/statesync/test/test_statesync.cpp	Adds regression test covering retry behavior after failed root validation.

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[Chen-Yifan]

approved but need to address copilot comments.