* glog: add gzip compression for rotated log files
Add opt-in gzip compression that automatically compresses log files
after rotation, reducing disk usage in long-running deployments.
- Add --log_compress flag to enable compression at startup
- Add SetCompressRotated()/IsCompressRotated() for runtime toggle
- Compress rotated files in background goroutine (non-blocking)
- Use gzip.BestSpeed for minimal CPU overhead
- Fix .gz file cleanup: TrimSuffix approach correctly counts
compressed files toward MaxFileCount limit
- Include 6 unit tests covering normal, empty, large, and edge cases
Enabled via --log_compress flag. Default behavior unchanged.
* glog: fix compressFile to check gz/dst close errors and use atomic rename
Write to a temp file (.gz.tmp) and rename atomically to prevent
exposing partial archives. Check gz.Close() and dst.Close() errors
to avoid deleting the original log when flush fails (e.g. ENOSPC).
Use defer for robust resource cleanup.
* glog: deduplicate .log/.log.gz pairs in rotation cleanup
During concurrent compression, both foo.log and foo.log.gz can exist
simultaneously. Count them as one entry against MaxFileCount to prevent
premature eviction of rotated logs.
* glog: use portable temp path in TestCompressFile_NonExistent
Replace hardcoded /nonexistent/path with t.TempDir() for portability.
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Co-authored-by: Copilot <copilot@github.com>
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