This commit improves the way processing status id is handled across different methods in the
ProcessingStatus module. Now, we consistently cast processing status id as string before passing it
to the config setter methods, eliminating any potential issues that might occur due to variable
type inconsistencies. Changes are applied to the Factory and Handler classes alike.

Related: #172

Improve readability and interpretability of code by explicitly stating null in union types. This
change has been applied across multiple files and functions.

PHP8.4 compatibility

fix: status change notification -> remove placeholder translation in message candyman-gmbh/projektplanung#109