Introduce ArrayBinaryOutput, BufferWriterBinaryOutput, BinaryOutputBase, and IBinaryOutput for flexible, efficient serialization to pooled arrays and streaming buffers. Refactor AcBinaryHubProtocol to use new output for SignalR. Make UseMetadata runtime-settable in AcBinarySerializerOptions. Update QuickBenchmark for new options. Enables allocation-free, extensible binary serialization infrastructure.
