fix(phpstan): improved method validity checks and reduced error handling

This commit fixes several issues in different PHP files.

• Added method_exists checks for isActive method in activate.php, deactivate.php and toggle.php to prevent calls to an undefined method.
• Similar check added for getTitle method in get.php.
• Fixed sorting functionality in search.php by using strcmp instead of greater than comparison.
• Removed a large number of ignored errors in phpstan-baseline.neon, indicating reduced error handling.
• Corrected the implode parameters order in Discount.php and typecasted variable to string before using explode in PriceFactor.php.
• Updated getTitle & toPriceFactor method parameters in Discount.php to use union types for compatibility with different data types.

Related: #18 (closed)