optimize(api): add warning logs for load-based request rejection

[contrueCT]

Purpose of the PR

• close [Improvement] Add critical log statements. #2747

Main Changes

Log busy-worker and low-memory rejections in LoadDetectFilter before returning ServiceUnavailableException so operators can diagnose 503 responses from server-side logs.

Add unit coverage for whitelist bypass, busy rejection,
low-memory rejection, and healthy request pass-through, and register the new test in UnitTestSuite.

Verifying these changes

• Trivial rework / code cleanup without any test coverage. (No Need)
• Already covered by existing tests, such as (please modify tests here).
• Need tests and can be verified as follows:
  • xxx

Does this PR potentially affect the following parts?

• Dependencies (add/update license info & regenerate_known_dependencies.sh)
• Modify configurations
• The public API
• Other affects (typed here)
• Nope

Documentation Status

• Doc - TODO
• Doc - Done
• Doc - No Need

[Copilot]

Pull request overview

Adds operator-visible warning logs when LoadDetectFilter rejects requests due to high worker load or low free memory (503s), and introduces unit tests to cover the new rejection behavior plus whitelist/healthy pass-through.

Changes:

• Add WARN logging for worker-load and low-memory request rejections in LoadDetectFilter.
• Add LoadDetectFilterTest unit coverage for whitelist bypass, busy rejection, low-memory rejection, and healthy requests.
• Register the new unit test in UnitTestSuite.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
hugegraph-server/hugegraph-api/src/main/java/org/apache/hugegraph/api/filter/LoadDetectFilter.java	Adds rejection WARN logs and minor refactor (captures current load).
hugegraph-server/hugegraph-test/src/main/java/org/apache/hugegraph/unit/api/filter/LoadDetectFilterTest.java	New unit tests for whitelist/busy/low-memory/healthy scenarios.
hugegraph-server/hugegraph-test/src/main/java/org/apache/hugegraph/unit/UnitTestSuite.java	Adds LoadDetectFilterTest to the unit suite.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

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[VGalaxies]

Thanks for the update. I left two small review comments; CI looks green on my side, but I think these are still worth addressing.

[contrueCT]

Thanks for the update. I left two small review comments; CI looks green on my side, but I think these are still worth addressing.

⚠️ The busy-load branch is rate-limited, but this low-memory WARN will still fire on every rejected request. Under sustained memory pressure that can flood the logs and add more I/O pressure to an already stressed server. Please apply the same REJECT_LOG_RATE_LIMITER here, or route both rejection logs through a shared sampling helper.
⚠️ This test drives the real System.gc() path by forcing the low-memory branch. That makes the suite slower and can make it behave differently on constrained CI nodes or JVMs with different GC ergonomics. Consider adding a test seam for the GC step so the test can stub it and only verify the rejection behavior.

Changes made:

• Applied the same reject-log rate limiting to the low-memory branch, and routed both rejection paths through a shared warning helper so the sampling behavior is consistent.
• Added a small test seam for gcIfNeeded() / reject-log sampling so the unit test no longer depends on a real System.gc() call.
• Expanded LoadDetectFilterTest to verify:
  • busy rejection emits a warning log
  • low-memory rejection emits a warning log
  • whitelist / healthy paths do not emit rejection logs
  • reject-log sampling suppresses repeated warning logs as expected