refactor: make routing/sending pipeline better and add optional telemetry

[PsiACE]

• introduce a unified router builder that lets agent/client handlers
  register request/notification methods declaratively, replacing bespoke
  dispatch logic
• reorganize connection internals around message queue, state store,
  dispatcher, and sender components for clearer responsibilities and easier
  injection
• add optional logfire/OpenTelemetry span instrumentation via span_context,
  wrapping request and notification execution without requiring
  configuration
• simplify supporting modules and remove legacy handlers while keeping
  existing tests (tests/test_rpc.py, tests/real_user) passing

This PR was primarily authored with GPT-5-Codex and hand-reviewed by me. I’m responsible for every change that lands here.

[phil65]

Cool. didnt test this yet, but the last commit already fixed the basic loop for me, I now have a fully functional python agent with filesystem client tools, terminal client tools, MCP support (including MCP -> ACP progress reporting) working.
Do you think that router system really improves things? Not really a fan of getattr magic...

[PsiACE]

but the last commit already fixed the basic loop for me

Glad the patch works for you—that was exactly why I shipped 0.4.5 yesterday after another user reported the issue.

Do you think that router system really improves things? Not really a fan of getattr magic...

As for the router: it’s mostly syntactic sugar to make handlers less painful. I get that the getattr-style magic isn’t everyone’s favorite. I’m considering a cleaner, more explicit approach and open to suggestions