feat: implement incoming connections

[markwylde]

This PR implements a comprehensive overhaul of WrapGuard to support incoming connections through a SOCKS5
proxy and WireGuard tunnel system. The changes include:

• SOCKS5 Proxy Implementation: Added a SOCKS5 proxy server to handle incoming connections and route
  traffic through the WireGuard tunnel
• Enhanced Configuration System: Restructured config parsing with better validation and wireguard-go
  compatibility
• Modernized Tunnel Management: Replaced custom network implementation with wireguard-go integration
  for better stability
• Structured Logging: Implemented JSON-based structured logging with configurable levels
• Docker Demo Environment: Added comprehensive demo showing Node.js applications communicating via
  WireGuard
• Improved Build System: Enhanced Makefile with cross-platform builds, testing, and development tools

Key Features

SOCKS5 Proxy Support

• Full SOCKS5 protocol implementation for handling incoming TCP connections
• Automatic traffic routing through WireGuard tunnel
• Support for both IPv4 and IPv6 connections

Enhanced WireGuard Integration

• Direct integration with wireguard-go library
• Proper TUN interface management
• Improved packet routing and handling
• Better error handling and connection stability

Docker Demo

• Complete Docker-based demonstration environment
• Shows real-world usage with Node.js HTTP servers
• Automated setup and key generation
• Cross-container communication through WireGuard tunnel

Technical Changes

Configuration System

• Converted config parser to use string-based fields for better compatibility
• Added base64 to hex conversion for wireguard-go IPC protocol
• Implemented hostname resolution for endpoints
• Enhanced validation with proper error messages

Logging System

• Replaced simple logging with structured JSON output
• Added configurable log levels (debug, info, warn, error)
• Included request/response logging for debugging
• Better error context and tracing

Build System

• Modernized Makefile with comprehensive targets
• Added cross-platform build support (Linux, macOS)
• Included testing, formatting, and linting tools
• Debug build configuration with symbols

Test Coverage

• Config parsing: Comprehensive tests for all configuration scenarios
• SOCKS5 proxy: Full protocol implementation testing
• Traffic forwarding: Bidirectional data flow validation
• Tunnel management: TUN interface and routing tests
• Logging system: Structured output and level filtering tests

Breaking Changes

• Configuration file format remains compatible but internal parsing has changed
• Command-line interface is preserved for backward compatibility
• C library interface updated for better integration

Demo Usage

cd demo
./setup.sh
docker compose up --build

This will start a WireGuard server and two Node.js applications that communicate through the tunnel without
 requiring root privileges or kernel modules.

Test Plan

- Build system works on Linux and macOS
- All unit tests pass (make test)
- Demo environment runs successfully
- SOCKS5 proxy handles connections correctly
- WireGuard tunnel establishes and routes traffic
- Configuration parsing works with existing configs
- Logging output is properly structured
- Cross-platform compatibility maintained