This commit refactors `MembershipUser.php` to improve code readability. It does this by including
spaces around the concatenation operators for better visual separation. This makes the identifiers
for verification checks much more readable.

The membership-related code was cleaned up across `getList.php`, `Handler.php`, `Membership.php`,
`Users/Handler.php`, and `Users/MembershipUser.php` files. Removed unnecessary comments and
@phpstan-ignore lines. Added strict type checking where it was missing and restructured some
conditions for better readability. Also, simplified the return statements in some methods.

This commit refactors several areas of the code to improve type definitions and error handling.
Main changes include:
- Improved the type definitions for function arguments and return types within the Handler,
Membership and Users Handler classes.
- Added error handling for instances where the Membership is not an instance of
QUI\Memberships\Membership.
- Updated the commenting style to more clearly define variables.
- Changed the use of \PDO to PDO for cleaner code.
- Removed unnecessary conditionals in the WHERE clause building of an SQL query, leading to
cleaner, more straightforward code.

- Removed redundant docblock.
- Added instance check for `$User` before attempting to remove it from groups to prevent potential
errors.
- Ensured `hasMembershipUserId` method exists before calling it to prevent undefined method errors.
- Adjusted `addHistoryEntry` function to receive a string as the second parameter instead of an
array.
- Removed redundant array-to-string conversion in `addHistoryEntry` function.
- Ignored `phpstan` warning regarding method's return type.

This commit addresses three major updates in our Memberships module:

1. In Handler.php, we clarified the return type of `isLinkedToContracts()` method by explicitly
defining it as boolean.
2. In AbstractMembershipUserLinkVerificationHandler.php, we simplified the Exception import and
updated the type in the `getMembershipUser()` method's doc comment.
3. In MembershipUser.php, the constructors for `CancelVerification` and `AbortCancelVerification`
are now called without the user id.

These changes enhance code readability and maintainability while ensuring safer calls.

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