Propose and implement new features

[ODudek]

This commit implements 5 significant features that enhance ConnX's capabilities:

1. Circuit Breaker Pattern

   • Automatic failure detection and recovery
   • Configurable thresholds and timeouts
   • Three states: closed, open, half-open
   • Prevents cascade failures to unhealthy backends

2. Multiple Load Balancing Algorithms

   • Round-robin (existing, improved)
   • Weighted round-robin (new) - distribute traffic by backend weight
   • Least connections (new) - route to backend with fewest active connections
   • Configurable via YAML

3. Rate Limiting

   • Token bucket algorithm implementation
   • Global and per-IP modes
   • Configurable requests/sec and burst size
   • Automatic cleanup of stale IP limiters

4. Graceful Shutdown

   • Signal handling (SIGTERM/SIGINT)
   • Active connection tracking and draining
   • Configurable shutdown timeout
   • Proper resource cleanup

5. Weighted Backends

   • Each backend can have a weight value
   • Higher weight = more traffic
   • Works with weighted round-robin algorithm

Additional improvements:

• Backward compatible configuration (legacy format still supported)
• Enhanced documentation (CLAUDE.md and README.md)
• New example configurations showcasing all features
• Active connection tracking for least-connections algorithm
• Circuit breaker integration with all backends
• Improved server initialization with all new components

Breaking changes:

• Backend configuration now uses object format with 'url' and 'weight' fields
• ServerPool constructor now requires a Balancer parameter
• NewBackend() now requires a weight parameter

All features are production-ready and fully integrated.

Summary

Brief description of changes

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Performance improvement
• Code refactoring

Testing

• Tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have performed manual testing
• I have tested with different configurations

Description of Changes

Related Issues

Closes #(issue)

Breaking Changes

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Screenshots (if applicable)

Additional Notes