test: feature_llmq_is_cl_conflicts.py intermittent ChainLock timeout under TSAN #7426

Failure

feature_llmq_is_cl_conflicts.py intermittently failed in linux64_tsan-test / Test source on a docs-only PR: https://github.com/dashpay/dash/actions/runs/28883252592/job/85680881154

The failing run retried the test three times and the final attempt timed out waiting for a ChainLock:

AssertionError: Predicate check_chainlocked_block not true after 60.0 seconds
File "test/functional/feature_llmq_is_cl_conflicts.py", line 256, in test_chainlock_overrides_islock_overrides_nonchainlock
    self.wait_for_chainlocked_block(node, cl_block.hash)

Scope

The PR that exposed this was #7410, which only changed AGENTS.md and CLAUDE.md. It did not touch source code, build logic, or functional tests, and the same head was merged afterward. This points to pre-existing/intermittent behavior in the test or ChainLock/InstantSend test timing under TSAN rather than a PR-caused regression.

There is an older closed issue for this test, #4542, but no currently open issue matched this failure mode.

Reproduction / follow-up

A useful starting point is to run the TSAN functional test target for feature_llmq_is_cl_conflicts.py repeatedly and inspect whether the final ChainLock wait in test_chainlock_overrides_islock_overrides_nonchainlock needs stronger synchronization before waiting for chainlock=true.

CI log seed from the failing final attempt: 2640902902445397136.