Last remaining enhancements and fixes for supporting natural gas data

[N3rdP1um23]

@jrfernandes Apologies for the delay. Though it's done and everything should be good to go now!

Here's an overview of the changes

• Upgraded workflow actions to use latest actions and updated flow
• Updated tests to use pytest and coverage across both electricity and natural gas sensors
• Refactored some of the code base
• Removed older data properties from OEB and added some of the new ones
• Resolved some issue with the unit of measure
• Updated the README to include additional writing, preview images, and badges to support latest changes
• Bumped integration to 0.4.1
• Fixed issue when attempting to unload an OEB entity from HomeAssistant

The following change should help

• Resolves #44
• Resolves #45
• Close #13

Let me know if you have any questions or concerns 😃