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]

The new WARN logs will be emitted for every rejected request; under overload this can produce a log storm and further degrade the server (I/O, disk, log rotation). Consider rate-limiting/sampling these rejection logs (similar to the existing RateLimiter usage elsewhere) or logging once per interval with aggregated counters.

[imbajin]

The new WARN logs will be emitted for every rejected request; under overload this can produce a log storm and further degrade the server (I/O, disk, log rotation). Consider rate-limiting/sampling these rejection logs (similar to the existing RateLimiter usage elsewhere) or logging once per interval with aggregated counters.

⚠️ 每次请求都会打印 WARN，可能产生大量日志 I/O，进一步放大系统抖动（导入/批量写入期间更明显）。

可以给“拒绝日志”加一个轻量限速（只限日志，不限请求处理），这样不会阻塞线程：

Suggested change

	if (currentLoad >= maxWorkerThreads) {
	LOG.warn("Rejected request due to high worker load, method={}, path={}, " +
	"currentLoad={}, maxWorkerThreads={}",
	context.getMethod(), context.getUriInfo().getPath(),
	currentLoad, maxWorkerThreads);
	if (REJECT_LOG_RATE_LIMITER.tryAcquire()) {
	LOG.warn("Rejected request due to high worker load, method={}, path={}, " +
	"currentLoad={}, maxWorkerThreads={}",
	context.getMethod(), context.getUriInfo().getPath(),
	currentLoad, maxWorkerThreads);
	}

// 每秒最多 1 条日志记录
参考：private static final RateLimiter REJECT_LOG_RATE_LIMITER = RateLimiter.create(1.0);

[Copilot]

This test injects private fields via a bespoke reflection helper. Since the codebase already has org.apache.hugegraph.testutil.Whitebox used in other tests for setting internal state, using it here (or centralizing the reflection helper) would reduce duplication and make the test less brittle if field names change.

[imbajin]

⚠️ 这里先 gcIfNeeded() 再记录日志，但当前日志里的 presumableFreeMem 是 GC 前快照。排障时容易误解为“GC 后仍然是这个值”。

建议同时输出 GC 前/后快照，定位会更直观：

Suggested change

	LOG.warn("Rejected request due to low free memory, method={}, path={}, " +
	gcIfNeeded();
	long allocatedMemAfterGc = Runtime.getRuntime().totalMemory() -
	Runtime.getRuntime().freeMemory();
	long freeMemAfterGc = (Runtime.getRuntime().maxMemory() -
	allocatedMemAfterGc) / Bytes.MB;
	LOG.warn("Rejected request due to low free memory, method={}, path={}, " +
	"presumableFreeMemMB(beforeGC)={}, presumableFreeMemMB(afterGC)={}, minFreeMemoryMB={}",
	context.getMethod(), context.getUriInfo().getPath(),
	presumableFreeMem, freeMemAfterGc, minFreeMemory);