PHPStan

[provokateurin]

TODO:

• fix(AppFramework): Adjust types so PHPStan understands them server#58098
• fix(CirclesManager): Use correct return type for probeCircles circles#2337
• fix(IRegistrationContext): Use SimpleContainer in registerService factory server#58261
• fix(IResult): Use more accurate conditional return type for fetchAll server#58256
• fix(IRegistrationContext): Use IContainer in registerService factory server#58355
• Fix a bunch of typing issues to make PHPStan level 10 happy on groupfolders server#58286
• Submit and backport bugs that were found separately
• Create GHA workflow
• Increase level even further

[provokateurin]

Still some things to do, but the code changes can be reviewed already.