fix a compaction induce latency issue

The compaction behavior is changed in commit
[02635](0263597) and introduces a latency issue.
To be more speicific, the `ticker.C` acts as a fixed timer that triggers every 10ms, regardless of how long each batch of compaction takes.
This means that if a previous compaction batch takes longer than 10ms, the next batch starts immediately, making compaction a blocking operation for etcd.

To fix the issue, this commit revert the compaction to the previous behavior which ensures a 10ms delay between each batch of compaction, allowing other read and write operations to proceed smoothly.

server/mvcc/kvstore_compaction.go

@@ -39,8 +39,6 @@ func (s *store) scheduleCompaction(compactMainRev, prevCompactRev int64) (KeyVal
 	binary.BigEndian.PutUint64(end, uint64(compactMainRev+1))
 
 	batchNum := s.cfg.CompactionBatchLimit
-	batchTicker := time.NewTicker(s.cfg.CompactionSleepInterval)
-	defer batchTicker.Stop()
 	h := newKVHasher(prevCompactRev, compactMainRev, keep)
 	last := make([]byte, 8+1+8)
 
@@ -90,7 +88,7 @@ func (s *store) scheduleCompaction(compactMainRev, prevCompactRev int64) (KeyVal
 		dbCompactionPauseMs.Observe(float64(time.Since(start) / time.Millisecond))
 
 		select {
-		case <-batchTicker.C:
+		case <-time.After(s.cfg.CompactionSleepInterval):
 		case <-s.stopc:
 			return KeyValueHash{}, fmt.Errorf("interrupted due to stop signal")
 		}