Implement GitHub-compatible 'gix push'

[stevei101]

Goal

Build a gix push command that is fully compatible with GitHub.

Requirements

• Support for GitHub's smart HTTP and SSH protocols.
• Seamless authentication using Git credential helpers.
• Robust and efficient pack file generation that adheres to GitHub's backend requirements.
• Reliable sideband-64k support for progress reporting.

This is part of the 'oxidized' initiative to provide high-performance, pure-Rust Git tooling.