General improvements to underlying codebase

[arabcoders]

This PR is mostly maintenance focused.

• Migrate to use mago for linting and formatting to standardize, as currently we use phpstorm, vscode, nvim etc and each platform has slightly different formatting.
• Focus more on testing the backends code, previously we mainly focused on integration testing for backends. This masks a real problem. Thus, i have improved the testing pipeline for each backend we support.
• This also fixes Null error after Jellyfin reinstall [BUG] #778 which happens sometimes when a backend is removed and references for it zeroed out from database.
• We also included minor memory improvement for Directmapper.
• Also fixed force import which if the time date is older than last item sync date would prevent it from actually changing local state.
• Also added minor feature to make it possible to target import specific library.
• Included a potential fix for jellyfin issue with not updating last played date after marking item as watched. The workaround is disabled by default, please refer to FAQ to know more.