Add authentication credential callback support

[emelialei88]

Summary

This PR adds support for authentication credential callbacks in the BlazingMQ Python SDK, enabling applications to provide dynamic authentication credentials when connecting to secured brokers.

New API Components

• BasicAuthnCredentialCb - Python wrapper class that accepts a callable returning (mechanism: str, data: bytes) or None
• FakeAuthnCredentialCb - Cython class that bridges Python callbacks to C++ authentication infrastructure
• authn_credential_cb parameter added to Session.__init__() and Session.with_options()

Implementation Details

• Integrated C++ authentication callback infrastructure with Python callable interface
• Implemented proper GIL management for cross-language callback invocation
• Added support for passing authentication credentials from Python to C++ BlazingMQ SDK
• Exposed get_credential_data() method for C++ to invoke Python callbacks

Example Usage

import blazingmq

def main() -> None:
    session = blazingmq.Session(
        blazingmq.session_events.log_session_event,
        authn_credential_cb=lambda: ("BASIC", b"python:sdk")
    ...