Add memory optimization improvements for reduced GC pressure (v0.36.16)

- Add buffer pool (pkg/database/bufpool) with SmallPool (64B) and MediumPool (1KB)
  for reusing bytes.Buffer instances on hot paths
- Fix escape analysis in index types (uint40, letter, word) by using fixed-size
  arrays instead of make() calls that escape to heap
- Add handler concurrency limiter (ORLY_MAX_HANDLERS_PER_CONN, default 100) to
  prevent unbounded goroutine growth under WebSocket load
- Add pre-allocation hints to Uint40s.Union/Intersection/Difference methods
- Update compact_event.go, save-event.go, serial_cache.go, and
  get-indexes-for-event.go to use pooled buffers

Files modified:
- app/config/config.go: Add MaxHandlersPerConnection config
- app/handle-websocket.go: Initialize handler semaphore
- app/listener.go: Add semaphore acquire/release in messageProcessor
- pkg/database/bufpool/pool.go: New buffer pool package
- pkg/database/compact_event.go: Use buffer pool, fix escape analysis
- pkg/database/get-indexes-for-event.go: Reuse single buffer for all indexes
- pkg/database/indexes/types/letter.go: Fixed array in UnmarshalRead
- pkg/database/indexes/types/uint40.go: Fixed arrays, pre-allocation hints
- pkg/database/indexes/types/word.go: Fixed array in UnmarshalRead
- pkg/database/save-event.go: Use buffer pool for key encoding
- pkg/database/serial_cache.go: Use buffer pool for lookups

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/handle-websocket.go

@@ -86,6 +86,12 @@ whitelist:
 	})
 
 	defer conn.Close()
+	// Determine handler semaphore size from config
+	handlerSemSize := s.Config.MaxHandlersPerConnection
+	if handlerSemSize <= 0 {
+		handlerSemSize = 100 // Default if not configured
+	}
+
 	listener := &Listener{
 		ctx:            ctx,
 		cancel:         cancel,
@@ -98,6 +104,7 @@ whitelist:
 		writeDone:      make(chan struct{}),
 		messageQueue:   make(chan messageRequest, 100), // Buffered channel for message processing
 		processingDone: make(chan struct{}),
+		handlerSem:     make(chan struct{}, handlerSemSize), // Limits concurrent handlers
 		subscriptions:  make(map[string]context.CancelFunc),
 	}