fix: enhance device handling in MiniBrew sensor integration

[stuartp44]

This pull request addresses issues with handling Device objects returned by the API in the MiniBrew Home Assistant integration, ensuring that both dictionary and object representations are processed correctly. The main changes improve robustness and compatibility when interacting with device data, preventing errors when the API returns Device instances instead of dictionaries.

Device data handling improvements:

• Added the _device_to_dict helper function in sensor.py to consistently convert Device objects or other representations into dictionaries for reliable attribute access.
• Updated all locations in sensor.py where device data is accessed (e.g., when checking the serial_number) to use _device_to_dict, ensuring compatibility with both dicts and Device objects. [1] [2] [3] [4] [5]

Bug fix:

• Fixed an issue where the integration would fail if the API returned Device objects without setup errors, as noted in the changelog.