Major performance improvements for SignalR message transport:
- BrotliHelper now uses ArrayPool and stackalloc for zero-allocation compression/decompression; added span/IBufferWriter overloads and pooled buffer support.
- AcJsonDeserializer supports direct deserialization from UTF-8 spans, with fast path for no reference handling.
- SignalResponseDataMessage uses pooled buffers for Brotli decompression and zero-copy deserialization; implements IDisposable for buffer return.
- IdMessage serialization optimized for primitives and Guids to avoid unnecessary allocations.
- Added JsonTo<T> span/byte[] extension methods for zero-allocation deserialization.
- All changes are backward compatible and reduce GC pressure for high-throughput scenarios.