Modernize the code

[jrauh01]

As we now use php 8.2 as minimal version, the following modernizations have been added to the code:

• Typed class properties
• Return values for methods
• Match expressions
• Modern string functions (e.g. str_contains(), str_starts_with() and str_ends_with())
• Nullsafe operator usage
• Deprecated code has been replaced
• Imports are now used everywhere

Additionally the import blocks have been sorted, indentation has been fixed, and some smaller adjustments.

resolves #378