chore(openssl): Update OpenSSL function signatures to use *mut instead of *const

[pluveto]

This PR updates the function signatures in the ext.rs file to use *mut instead of *const for the ssl and cert parameters in the SSL_use_certificate and SSL_use_PrivateKey functions. This indicates that the functions can modify the SSL and certificate objects as intended.

Ref:

• https://www.openssl.org/docs/man1.1.1/man3/SSL_use_certificate.html
• https://boringssl.googlesource.com/boringssl/+/refs/tags/fips-20180730/ssl/ssl_cert.cc#292

Refactor the cvt function to use c_long instead of c_int for the return type for better compatibility with the types used in the OpenSSL library.

Also, add a test case for the ssl_set_groups_list function to ensure it handles valid and invalid input correctly.