Add Python, Go, and .NET e2e tests for agent selection and compaction APIs

- Regenerate RPC types for Python, Go, and .NET from updated schema
- Add e2e tests for all 3 languages matching Node.js test patterns
- Fix C# codegen request class name collisions (use full RPC method path)
- Update dotnet/src/Generated/SessionEvents.cs and go/generated_session_events.go

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: SteveSandersonMS