Implement simple HAProxy Protocol v2 support

[colbster937]

📌 Pull Request

Description

This allows servers to accept PROXY protocol v2 headers to preserve the original client IP.

Related Issues / Discussions

• Fixes Haproxy support #40
• Fixes Add HAProxy's Proxy Protocol Support #74

Motivation & Context

This is useful for setups where the server is running behind a proxy, such as load balancing a poseidon server across multiple ips, or in cases like mine where my server is self hosted without port forwarding but still needs access to the original client IPs.

Type of Change

Please tick all that apply:

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ⚡ Performance improvement
• 🧩 New feature (non-breaking)
• 🔧 Refactor / cleanup (no functional changes)
• 🔥 Crash / exploit fix
• 📚 Documentation update
• ❗ Breaking change (may affect plugins or server behavior)

Testing Performed

• Compiled successfully with mvn clean package
• Tested on a Beta 1.7.3 server
• Existing functionality verified
• Edge cases considered

Test details:

Tested locally with NGINX using PROXY protocol v2 enabled, and normally with PROXY protocol v2 disabled.

Compatibility Considerations

• No known compatibility impact
• Potential plugin impact (described below)
• Network / protocol (Netcode) behavior changed
• Configuration change required

Compatibility Notes

Checklist

Please confirm the following:

• No unnecessary formatting or whitespace-only changes
• Changes are compatible with Minecraft Beta 1.7.3
• No dependencies have been added without discussion with the RetroMC team

Thanks for contributing to Project Poseidon!