fix: correct unique_id generation for KegSensor and KegOnlineStatusSensor

[stuartp44]

This pull request makes small improvements to the KegSensor class in custom_components/minibrew/sensor.py to ensure consistent use of the device identifier and simplify the generation of unique IDs.

Most important changes:

Device identifier consistency:

• The __init__ method now sets self.device to the passed device object, ensuring it is available throughout the class.

Unique ID generation:

• The unique_id property now consistently uses self.device_id instead of directly accessing self.device.serial_number, simplifying the code and reducing redundancy. [1] [2]

Closes #9

[github-actions]

Preview Release Created

A preview release has been created for testing this PR.

Version: 0.6.0-preview.10.f7ccb10
Release: https://github.com/stuartp44/hambrewclient/releases/tag/v0.6.0-preview.10.f7ccb10

How to Test

1. Go to the draft release
2. Download minibrew-0.6.0-preview.10.f7ccb10.zip
3. Extract to your Home Assistant custom_components directory
4. Restart Home Assistant
5. Test the changes and report back here

Or install directly via HACS:

# Add custom repository in HACS:
https://github.com/stuartp44/hambrewclient

# Then select version: 0.6.0-preview.10.f7ccb10

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WARNING: This is a preview release - do not use in production!

Once testing is complete and approved, this PR can be merged for an official release.