fix(mqtt): split reconnect loop handler to reduce log noise

[cayossarian]

Summary

• Splits the single except Exception handler in SpanMqttClient._reconnect_loop into two branches: expected transient failures (OSError family — ConnectionRefusedError, socket.gaierror, TimeoutError, ssl.SSLError) log a one-line WARNING with the exception repr; unexpected exceptions retain the full traceback via exc_info=True.
• The common "panel offline" case (e.g. ConnectionRefusedError: [Errno 61]) no longer floods logs with paho/stdlib stack frames that carry no diagnostic signal — the exception type and errno are the full diagnostic.
• Unknown exceptions still surface full tracebacks so support tickets remain actionable.
• Bumps version to 2.6.2.

Rationale

Pre-change log on panel disconnect:

WARNING ... Reconnect failed, retrying in 60.0s
Traceback (most recent call last):
  File ".../connection.py", line 409, in _reconnect_loop
    await self._loop.run_in_executor(None, self._client.reconnect)
  File ".../paho/mqtt/client.py", line 1598, in reconnect
  File ".../paho/mqtt/client.py", line 4609, in _create_socket
  File ".../paho/mqtt/client.py", line 4640, in _create_socket_connection
  File ".../socket.py", line 870, in create_connection
  File ".../socket.py", line 855, in create_connection
ConnectionRefusedError: [Errno 61] Connection refused

Every frame is paho/stdlib internals that are identical on every such failure. The last line is the only signal.

Post-change log:

WARNING ... Reconnect failed (ConnectionRefusedError(61, 'Connection refused')), retrying in 60.0s

Note: ssl.SSLError is an OSError subclass and falls into the transient branch — deliberate, since SSL misconfiguration fails at setup (async_setup_entry), not at reconnect. A reconnect-time SSL failure is treated as transient alongside the other network errors.

Test plan

• All 343 existing tests pass (pre-commit coverage gate green at 96.16%)
• All lint hooks pass (ruff, black, prettier, mypy, pylint, bandit, vulture, markdownlint, uv lock check)
• Manual verification: take panel offline, observe single-line WARNING without paho/stdlib frames
• Manual verification: force an unexpected exception path, confirm traceback still present