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/config/config.go

@@ -106,6 +106,9 @@ type C struct {
 	SerialCachePubkeys  int `env:"ORLY_SERIAL_CACHE_PUBKEYS" default:"100000" usage:"max pubkeys to cache for compact event storage (default: 100000, ~3.2MB memory)"`
 	SerialCacheEventIds int `env:"ORLY_SERIAL_CACHE_EVENT_IDS" default:"500000" usage:"max event IDs to cache for compact event storage (default: 500000, ~16MB memory)"`
 
+	// Connection concurrency control
+	MaxHandlersPerConnection int `env:"ORLY_MAX_HANDLERS_PER_CONN" default:"100" usage:"max concurrent message handlers per WebSocket connection (limits goroutine growth under load)"`
+
 	// Adaptive rate limiting (PID-controlled)
 	RateLimitEnabled            bool    `env:"ORLY_RATE_LIMIT_ENABLED" default:"true" usage:"enable adaptive PID-controlled rate limiting for database operations"`
 	RateLimitTargetMB           int     `env:"ORLY_RATE_LIMIT_TARGET_MB" default:"0" usage:"target memory limit in MB (0=auto-detect: 66% of available, min 500MB)"`