This commit improves the type consistency and readability of the code in the Membership class and
related classes. The changes include adding strict types, removing unused imports, using type
hinting, and replacing old switch-case syntax with match expressions.

Specifically, it changes the signature of several functions, adds and removes some class imports,
and replaces old style function syntax with modern type hinting for better readability and
maintainability. Moreover, it adds PHP built-in functions instead of using their fully qualified
form. It also improves readability by replacing the switch-case syntax with the new and more
convenient match expression when parsing intervals from the duration.

refactor: date calculation when linked with contracts

fix: check if a user exists first before trying to delete him from QUIQQER groups when archiving namerobot/tool#35