feat: Add ability to listen for ready devices

[allenporter]

Add a callback that will be invoked when devices become ready. This is to allow non-blocking setup with dynamically connected devices. In the future we can periodically or asynchronously invoke discover_devices and automatically find new devices as they become available.

[Copilot]

Pull request overview

This PR adds a ready callback mechanism to notify consumers when Roborock devices become ready for use. This enables non-blocking device setup and lays groundwork for future dynamic device discovery.

Key changes:

• Introduces DeviceReadyCallback type and add_ready_callback method on RoborockDevice
• Integrates ready callback into create_device_manager for automatic notification when devices connect
• Adds comprehensive test coverage for the ready callback feature

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
roborock/devices/device.py	Adds DeviceReadyCallback type, add_ready_callback method, and integrates callback invocation into connection logic; also increases START_ATTEMPT_TIMEOUT
roborock/devices/device_manager.py	Adds ready_callback parameter to create_device_manager and wires it to newly created devices
tests/devices/test_device_manager.py	Adds test_ready_callback test and updates test_start_connect_failure to verify callback behavior with connection failures and retries

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