Make thread monitoring opt-in, harden ThreadMonitor, and remove sleep from async backoff handler

[Thunderrock424242]

Motivation

• Reduce noise and runtime overhead by making the thread monitor conditional on configuration and by avoiding needless sleeps in the async backoff path.
• Improve robustness of the thread monitor so it won't spawn multiple instances and will stop cleanly on shutdown.

Description

• Wrapped ThreadMonitor.startMonitoring() in NovaAPI with a guard based on NovaAPIConfig.isMemoryThreadLogsEnabled() so monitoring only starts when enabled.
• Reworked ThreadMonitor to prevent multiple monitor instances, run the monitor thread as a daemon, handle interruptions cleanly, and stop via a running flag in stopMonitoring().
• Optimized ThreadMonitor.logAllThreads() to use ThreadMXBean for a lightweight thread count and only gather per-thread stack traces when trace logging is enabled, and to respect NovaAPIConfig.isMemoryThreadLogsEnabled().
• Enhanced deadlock detection in ThreadMonitor.checkForDeadlocks() using ThreadMXBean.findDeadlockedThreads() and improved logging of detected deadlocks.
• Removed the 5ms Thread.sleep backoff from the callerRunsWithBackoff handler in AsyncTaskManager so caller-run fallback executes immediately without sleeping.

Testing

• Ran ./gradlew test and ./gradlew build as the project automated checks, and the build and test suite completed successfully.
• Verified the code compiles and the modified classes load in the test environment without runtime exceptions during startup.
• Automated unit tests covering async executor behavior and thread utilities passed (no failures).

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Start monitor when thread-log config is toggled on

Gating ThreadMonitor.startMonitoring() to server startup means enableMemoryThreadLogs can no longer be enabled dynamically: with the default false, the monitor thread never starts, and onConfigReload (same file) does not start it later, so thread/deadlock monitoring remains disabled until a full server restart. Before this change, the monitor was already running and the config flag took effect on the next cycle.

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