[Task] Backend refactoring / Code style

## Why?

The backend has not seen a code refresh in a long time, and due to the very unstable nature of what we did (implement theme switching which is not sanctioned in any way and required a lot of hacky workarounds that weren't part of the equation when the components were designed) the code quality leaves much to be desired in quite a lot of areas of the code.

## How?

For 11.1, I would propose to refactor the backend to
- Bring it up to speed with the newest C# conventions
- Define conventions we would like to use going forward in the project
- Create automatic linting that conforms to our standards

In order to do this, we need to have an in-depth discussion of what our code style is supposed to look like.
Let's tackle this one convention / suggestion at a time and use this issue to keep track of our changes.

I'll start a checklist here which will contain all of our findings.
We can then go ahead and implement each of the respective conventions in a PR.

@Armin2208, @Jay-o-Way, @ChenYiLins please let me know if you would like to participate in this task.

## Place for discussions

Let's use this issue for comments related to the implementation only, and move the rest to
https://github.com/AutoDarkMode/Windows-Auto-Night-Mode/discussions/1041