* Replace non-unicode characters for add-on static files
Add-on documentation and changelog get read and returned as text file.
However, in case the original author used non-unicode characters, or
the file corrupted, loading currently fails with an UnicodeDecodeError.
Let's just use the built-in replace error handling of Python, so they
appear for the user as non-unicode characters by replacing them with
the official unicode replacement character "�".
* Remove superflous parameter for binary files
* ruff format
* Add pytests