glog: add --log_rotate_hours flag for time-based log rotation (#8685)

* glog: add --log_rotate_hours flag for time-based log rotation

SeaweedFS previously only rotated log files when they reached MaxSize
(1.8 GB). Long-running deployments with low log volume could accumulate
log files indefinitely with no way to force rotation on a schedule.

This change adds the --log_rotate_hours flag. When set to a non-zero
value, the current log file is rotated once it has been open for the
specified number of hours, regardless of its size.

Implementation details:
- New flag --log_rotate_hours (int, default 0 = disabled) in glog_file.go
- Added createdAt time.Time field to syncBuffer to track file open time
- rotateFile() sets createdAt to the time the new file is opened
- Write() checks elapsed time and triggers rotation when the threshold
  is exceeded, consistent with the existing size-based check

This resolves the long-standing request for time-based rotation and
helps prevent unbounded log accumulation in /tmp on production systems.

Related: #3455, #5763, #8336

* glog: default log_rotate_hours to 168 (7 days)

Enable time-based rotation by default so log files don't accumulate
indefinitely in long-running deployments. Set to 0 to disable.

* glog: simplify rotation logic by combining size and time conditions

Merge the two separate rotation checks into a single block to
eliminate duplicated rotateFile error handling.

* glog: use timeNow() in syncBuffer.Write and add time-based rotation test

Use the existing testable timeNow variable instead of time.Now() in
syncBuffer.Write so that time-based rotation can be tested with a
mocked clock.

Add TestTimeBasedRollover that verifies:
- no rotation occurs before the interval elapses
- rotation triggers after the configured hours

---------

Co-authored-by: Copilot <copilot@github.com>

weed/glog/glog_file.go

@@ -57,6 +57,13 @@ var logMaxSizeMB = flag.Uint64("log_max_size_mb", 1800, "Maximum size in megabyt
 // Defaults to 5.
 var logMaxFiles = flag.Int("log_max_files", 5, "Maximum number of log files to keep per severity level before older ones are deleted (0 = use default of 5)")
 
+// logRotateHours controls time-based log rotation.
+// When non-zero, each log file is rotated after the given number of hours
+// regardless of its size. This prevents log files from accumulating in
+// long-running deployments even when log volume is low.
+// The default is 168 hours (7 days). Set to 0 to disable time-based rotation.
+var logRotateHours = flag.Int("log_rotate_hours", 168, "Rotate log files after this many hours (default: 168 = 7 days, 0 = disabled)")
+
 func createLogDirs() {
 	// Apply flag values now that flags have been parsed.
 	if *logMaxSizeMB > 0 {
@@ -73,6 +80,12 @@ func createLogDirs() {
 	}
 }
 
+// LogRotateHours returns the configured time-based rotation interval.
+// This is used by syncBuffer to decide when to rotate open log files.
+func LogRotateHours() int {
+	return *logRotateHours
+}
+
 var (
 	pid      = os.Getpid()
 	program  = filepath.Base(os.Args[0])