Refactor Callback Tests for Improved Memory Management

Refactor the callback test code to replace global variables with local structures, enhancing memory management and reducing reliance on redundant cleanup logic.

Using a local struct containing a magic number and result flag to ensure the correct handling of user data and to verify that the callback function is invoked at least once during the test.

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/25330)

(cherry picked from commit 9808ccc5)