Introduce diagnostic and test infrastructure for SignalR binary protocol serialization/deserialization, including:
- ProtocolRoundTripDiagnosticTest for isolated protocol byte inspection
- TestMultiSegmentProtocol to exercise multi-segment buffer parsing
- TestInvocationBinder for correct parameter type binding
- Updates to TestableSignalRClient2 and TestableSignalRHub2 to route all messages through protocol round-trip
- Enhanced SendMessageToClient to simulate real SignalR transport
- Clarified SequenceBinaryInput segment handling logic
- Made TryParseMessage virtual in AcBinaryHubProtocol for testability
These changes improve test coverage for cross-boundary and multi-segment scenarios in SignalR message handling.
