refactor(test): Move straggler tests to unit tests and reduce to 10 focused tests

Changes:
- Moved tests from E2E to Unit (were unit tests, not E2E)
- Reduced from 30 redundant tests to 10 critical tests
- Removed obvious tests (parameter validation, basic getters/setters)

Unit tests now focus on:
- Duplicate detection prevention across monitoring cycles
- Atomic CTS replacement for retries
- Cleanup execution in finally blocks
- Cleanup cancellation during shutdown
- Concurrent cleanup safety
- Counter overflow protection (long vs int)
- Median calculation correctness (even/odd count)
- Empty metrics null safety
- Concurrent modification thread safety

All 10 tests pass.

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Co-Authored-By: Claude <noreply@anthropic.com>

Author: msrathore-db