Complete WriteBufferManager Java API with monitoring methods

[mike-evolved]

Summary

Adds 10 missing methods to WriteBufferManager Java API.

Changes

• Monitoring: enabled(), costToCache(), memoryUsage(), mutableMemtableMemoryUsage(), dummyEntriesInCacheUsage(), bufferSize()
• Control: setBufferSize(), setAllowStall()
• Status: isStallActive(), isStallThresholdExceeded()
• tests

Previously Java users could only create WriteBufferManager but couldn't monitor memory usage or adjust settings.

Example

try (WriteBufferManager wbm = new WriteBufferManager(32 * MB, cache, true)) {
    System.out.println("Memory: " + wbm.memoryUsage() + " / " + wbm.bufferSize());
    if (wbm.isStallThresholdExceeded()) wbm.setBufferSize(64 * MB);
}

[github-actions]

✅ clang-tidy: No findings on changed lines

Completed in 0.0s.

[meta-codesync]

@hx235 has imported this pull request. If you are a Meta employee, you can view this in D95603876.

[hx235]

Could you fix the format error https://github.com/facebook/rocksdb/actions/runs/22458935067/job/65833367780?pr=14392 others look good to me.