Connection._run_notification wrapped the handler call in
contextlib.suppress(Exception), swallowing every notification-handler
error silently: no log, and (correctly) no wire response since
notifications have none by protocol. It was the only handler-error path
in the module that stayed silent — main_loop, the receive loop, stream
observers, _on_receive_error, _on_task_error, and (since the previous
commit) _run_request all log. Integrators wiring Sentry via the logging
integration therefore had to wrap every notification handler (cancel,
ext_notification, and on the client side session_update,
complete_elicitation) by hand to see failures.

Replace the suppress with a try/except that logs the original exception
and its traceback, mirroring the logging.exception(..., exc_info=exc)
call in _run_request. Behaviour is otherwise unchanged: the exception is
still not propagated, and the telemetry span still sees no exception
(contextlib.suppress already exited before span_context, so this is not a
span-status change). Unlike _run_request we deliberately do not re-raise:
notifications have no response and no store bookkeeping, so re-raising
would only add a duplicate, contextless "Background task failed" line.

Drop the now-unused contextlib import.

Adds a regression test: a session/cancel handler that raises is logged
(with traceback) instead of silently swallowed.

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

Rewrites the request/notification error-logging tests to be deterministic
and precise instead of only asserting that "some record has exc_info":

- Drive Connection._run_request / _run_notification directly with a
  recording sender (mirroring test_core's TrackingSender) so assertions
  cover the exact wire frame: a request emits one -32603 error carrying
  {"details": ...} and re-raises RequestError; a notification emits
  nothing (deterministic, no timeout read).
- Assert the logged record is the original RuntimeError (type + message)
  under the expected method=..., not merely that a record exists.

Confirmed both tests fail on the pre-fix behaviour (silent suppress / no
request log) and pass with it.

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>