Fixes#31169
The TestTransactionForgotten test was flaky due to real time
dependencies. This PR:
- Replaces real time with mock clock for deterministic timing control
- Adds precise state checks at timeout boundaries
- Verifies underpriced cache states and cleanup
- Improves test reliability by controlling transaction timestamps
- Adds checks for transaction re-enqueueing behavior
The changes ensure consistent test behavior without timing-related
flakiness.
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Co-authored-by: Zsolt Felfoldi <zsfelfoldi@gmail.com>