`SamATM90E26_library` is not a library

Currently, we have a library called `SamATM90E26_library` in our Library directory. However,

- It looks like the code is essentially coming from here: https://github.com/whatnick/ATM90E26_Arduino but not reference is provided
- This code is not used as a library, but instead users actually need to chance the code as part of the calibration process, see [here](https://github.com/EnAccess/OpenSmartMeter/blob/main/README.md?plain=1#L121)

This can cause a lot of confusion amongst users and should be cleaned up.

This consists of two steps

1. First, move the code from `Library` folder into the main folder of the code to signal this custom code is part of the Firmware and subject to changes.
2. Refactor the code to re-use as much code from https://github.com/whatnick/ATM90E26_Arduino and move the customisations as part of the calibration into a more clear location.