Add test for BIO password callback functionality

Related to #8441

This commit introduces a test suite for the password callback mechanism used when reading or writing encrypted and PEM or DER encoded keys via a BIO in OpenSSL. The test is designed to cover various edge cases, particularly focusing on scenarios where the password callback might return unexpected or malformed data from user code.

By simulating different callback behaviors, including negative returns, zero-length passwords, passwords that exactly fill the buffer and wrongly reported lengths. Also testing for the correct behaviour of binary passwords that contain a null byte in the middle.

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