feat: conformance test runner + protocol fixes

- conformance.py: declarative scenario runner (subset matcher, $kind/$gt/
  $enum/$required assertions, call_id/session_id echo checks), reference
  bridge, CLI entry (python -m aicc.conformance)
- bridge.py: protocol version check before parsing (protocol_mismatch),
  session expiry handling (session_expired), malformed tool_call ->
  invalid_input, emit_event() for async events
- client.py: Self return type
- in_process.py: drain bridge event queue after response (event delivery),
  Self return type
- websocket.py: Self return type, best-effort shutdown
- tests: 14 passing (incl. conformance scenarios, 9/9 core scenarios)
- ruff: all checks pass

aicc/transport/__init__.py

@@ -3,7 +3,7 @@
 from aicc.transport.base import Transport
 from aicc.transport.in_process import InProcessTransport
 
-__all__ = ["Transport", "InProcessTransport"]
+__all__ = ["InProcessTransport", "Transport"]
 
 try:  # pragma: no cover
     from aicc.transport.websocket import WebSocketClientTransport, WebSocketServer