fix(Session): clear session data on destroy in testing environment

[gr8man]

Description
In the testing environment, Session::destroy() returned early without calling session_destroy(). While avoiding raw PHP session functions in CLI/testing is expected, doing nothing meant that the mock session data stored in the $_SESSION superglobal remained completely intact. This caused session state to leak between test cases, leading to test pollution.

This PR addresses the issue by resetting the $_SESSION array ($_SESSION = []) when destroy() is called under the testing environment. A unit test has also been added to verify this behavior.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide