Add New SSL Native API Test Cases

[pepone]

This PR adds four new test cases for SSL native APIs and includes minor test cleanup:

1. clientValidatesServerUsingValidationCallback:

   • Verifies that the client can use a validation callback to accept a certificate that would otherwise be rejected.

2. clientValidatesServerUsingSystemTrustedRootCertificates:

   • Tests the client's ability to validate zeroc.com certificates using default system Certificate Authorities (CAs).

3. serverValidatesClientUsingValidationCallback:

   • Client-side counterpart of clientValidatesServerUsingValidationCallback, ensuring that the server can use a validation callback to accept client certificates.

4. serverHotCertificateReload:

   • Tests the server's ability to reload certificates without restarting.