Add a hook for handling background rate limit errors

[allenporter]

When a rate limit error is received the background loop will jump to the maximum backoff (now 6 hours) and will also invoke a callback so that the caller can decide to re-authenticate or stop harder.

The new backoff follows this trajectory, where the change in behavior is introduced after 15 attempts:

• attempt 1: wait 10 seconds
• attempt 5: waits 50 seconds
• attempt 7: waits 2 minutes
• attempt 10: waits 6 minutes
• attempt 15: waits 32 minutes
• attempt 17: waits 2 hours
• attempt 20: waits 6 hours

[Copilot]

Pull request overview

This PR adds a callback hook mechanism for handling MQTT unauthorized/rate-limit errors and increases the maximum backoff interval from 30 minutes to 6 hours to better handle persistent authentication issues.

Key Changes:

• Adds SessionUnauthorizedHook callback type and unauthorized_hook parameter to MqttParams for notification of rate limit/unauthorized errors
• Increases MAX_BACKOFF_INTERVAL from 30 minutes to 6 hours, allowing the background reconnection loop to back off more aggressively for persistent failures
• Invokes the hook when MQTT code 135 (unauthorized) is received, and sets backoff to maximum to prevent rapid retry attempts

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
roborock/mqtt/session.py	Defines the SessionUnauthorizedHook type alias and adds the unauthorized_hook field to MqttParams with documentation
roborock/mqtt/roborock_session.py	Updates max backoff interval to 6 hours, stores the hook from params, invokes it when unauthorized errors occur, and adds error-specific diagnostics
roborock/devices/device_manager.py	Adds mqtt_session_unauthorized_hook parameter to create_device_manager and propagates it to MQTT params
tests/mqtt/test_roborock_session.py	Refactors MQTT client fixtures for better testability and adds tests for unauthorized hook behavior during initial connection and reconnection

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