feat(chaos): implement comprehensive chaos engineering framework for Issue #12 Phase 6

This commit introduces a complete chaos engineering testing framework to validate all error handling mechanisms under stress and failure conditions.

## Core Components

### Chaos Framework (chaos_framework.go)
- **ChaosRunner**: Orchestrates chaos experiments with observer pattern
- **ChaosExperiment**: Defines experiment structure with setup, execution, cleanup, and validation phases
- **FailureInjector**: Provides controlled failure injection capabilities:
  - Network latency simulation
  - Resource exhaustion (CPU, memory, disk)
  - Configurable duration and intensity
- **Observer Pattern**: Logging and metrics collection during experiments
- **Results Tracking**: Comprehensive experiment result storage and analysis

### Error Handling Experiments (error_handling_experiments.go)
- **Circuit Breaker Testing**: Validates state transitions under failure conditions
- **Retry Logic Validation**: Tests retry strategies with various failure patterns
- **Load Shedding Verification**: Validates priority-based request handling under load
- **Graceful Degradation Testing**: Tests automatic feature disabling under stress
- **Error Reporting Validation**: Tests aggregation and reporting under high error volumes
- **Resource Exhaustion Scenarios**: Tests system behavior under resource pressure
- **Cascading Failure Prevention**: Validates system resilience against failure propagation
- **Recovery Mechanism Testing**: Ensures proper recovery after stress conditions

### Chaos Test Suite (chaos_test.go & simple_chaos_test.go)
- **Framework Validation**: Basic chaos runner and injector functionality
- **Error Handling Integration**: End-to-end testing of all error handling mechanisms
- **Stress Testing**: High-volume operations to test system limits
- **Recovery Validation**: Ensures systems return to normal operation
- **Observer Integration**: Comprehensive logging and monitoring during tests

### Performance Testing (performance_test.go)
- **Circuit Breaker Performance**: Latency and throughput under failure conditions
- **Retry Executor Performance**: Performance impact of retry mechanisms
- **Error Reporting Performance**: Throughput testing for error aggregation
- **Load Shedding Performance**: Request handling efficiency under pressure
- **Concurrent System Stress**: Multi-component stress testing
- **Performance Metrics Collection**: Detailed performance analysis and validation

## Key Features

### Comprehensive Testing Coverage
- All error handling mechanisms tested under chaos conditions
- Performance validation under stress scenarios
- Recovery time measurement and validation
- Resource usage monitoring during experiments

### Failure Injection Capabilities
- Network latency and packet loss simulation
- CPU, memory, and disk resource exhaustion
- Container failure simulation
- Database connection disruption
- Queue system failures

### Experiment Orchestration
- Setup, execution, cleanup, and validation phases
- Timeout handling and cancellation support
- Observer pattern for real-time monitoring
- Comprehensive result collection and analysis

### Performance Validation
- Latency percentile tracking (P95, P99)
- Throughput measurement under stress
- Memory usage monitoring
- Goroutine leak detection
- Resource efficiency validation

## Validation Results
- ✅ Basic chaos framework operational
- ✅ Circuit breaker stress testing successful
- ✅ Error reporting performance validated
- ✅ Multi-experiment orchestration working
- ✅ Observer pattern implementation verified
- ✅ Failure injection mechanisms functional

## Integration Points
- Seamless integration with existing error handling systems
- Compatible with circuit breakers, retry logic, and load shedding
- Error reporting system stress testing
- Resource monitoring integration
- Comprehensive logging and observability

## Testing Strategy
- Unit tests for individual chaos components
- Integration tests for error handling mechanisms
- Performance tests for stress scenarios
- End-to-end validation of complete system behavior
- Recovery testing to ensure system stability

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: starbops