Add Canonical JSON serialization library with tests and documentation

- Implemented CanonJson class for deterministic JSON serialization and hashing.
- Added unit tests for CanonJson functionality, covering various scenarios including key sorting, handling of nested objects, arrays, and special characters.
- Created project files for the Canonical JSON library and its tests, including necessary package references.
- Added README.md for library usage and API reference.
- Introduced RabbitMqIntegrationFactAttribute for conditional RabbitMQ integration tests.

examples/router/src/Examples.Gateway/Program.cs

@@ -22,6 +22,9 @@ builder.Services.AddInMemoryTransport();
 // Authority integration (no-op for demo)
 builder.Services.AddNoOpAuthorityIntegration();
 
+// Required for app.UseAuthentication() even when running without a real auth scheme (demo/tests).
+builder.Services.AddAuthentication();
+
 var app = builder.Build();
 
 // Middleware pipeline