GWS Files

perf: optimize buffer pool and writer path, harden RFC compliance

• Replace map-based BufferPool with [32]sync.Pool using bit operations
• Refactor Payload to concrete struct to achieve zero heap allocations on writes
• Optimize deflater to eliminate intermediate buffer copy during decompression
• Fix connector goroutine leak on handshake timeout
• Validate RSV bits on control and continuation frames per RFC 6455/7692
• Enforce MSB=0 check on 64-bit frame lengths to prevent integer overflow
• Remove sync.Mutex from RandomString using Go 1.20+ thread-safe math/rand