chore: add comprehensive error handling and logging infrastructure

[1234-ad]

Summary

Adds comprehensive error handling infrastructure with custom exceptions, centralized logging, and retry mechanisms for resilient API calls.

Changes

pr_review/exceptions.py

Custom exception hierarchy:

• PRReviewError: Base exception for all PR review errors
• GitHubAPIError: GitHub API failures with status code tracking
• MetricsCalculationError: Metrics computation failures
• AILabelingError: AI labeling service failures
• ReviewerAssignmentError: Reviewer assignment failures
• DiscordNotificationError: Discord notification failures
• ConfigurationError: Configuration validation errors
• ValidationError: Input validation errors

pr_review/logging_config.py

Centralized logging utilities:

• setup_logging(): Configure logging with console and file output
• Rotating file handler with configurable size and backup count
• LoggerMixin: Add logging to any class via inheritance
• LogLevel: Context manager for temporary log level changes
• Structured log format with filename and line numbers

pr_review/utils/retry_utils.py

Retry and resilience utilities:

• @retry: Decorator for sync functions with exponential backoff
• @retry_async: Decorator for async functions with exponential backoff
• CircuitBreaker: Prevent cascading failures with circuit breaker pattern
• Configurable retry attempts, delays, and backoff multipliers
• Custom exception handling and retry callbacks

Benefits

• ✅ Better error categorization and handling
• ✅ Easier debugging with specific exception types
• ✅ Consistent logging across all modules
• ✅ Resilient API calls that handle transient failures
• ✅ Exponential backoff prevents overwhelming failing services
• ✅ Circuit breaker prevents cascading failures
• ✅ Production-ready reliability patterns
• ✅ Improved error messages and context

Usage Examples

# Custom exceptions
from exceptions import GitHubAPIError
raise GitHubAPIError("API rate limit exceeded", status_code=429)

# Logging
from logging_config import setup_logging, LoggerMixin
logger = setup_logging('my_module', level='DEBUG', log_file='logs/app.log')

# Retry decorator
from utils.retry_utils import retry
@retry(max_attempts=3, delay=1.0, backoff=2.0)
def fetch_github_data():
    return github_client.get_pull_request(repo, pr_number)

# Circuit breaker
breaker = CircuitBreaker(failure_threshold=5, recovery_timeout=60.0)
result = breaker.call(risky_api_call, arg1, arg2)

Testing

• All utilities tested with Python 3.13
• Exception hierarchy validated
• Logging configuration tested with file rotation
• Retry logic tested with mock failures

Impact

• Significantly improves error handling reliability
• Better debugging and troubleshooting capabilities
• More resilient to transient failures
• Production-ready error handling patterns