Add singleton logging configuration for the renamer application

This commit introduces a new module `logging_config.py` that implements a singleton pattern for logging configuration. The logger is initialized only once and can be configured based on an environment variable to log to a file or to the console. This centralizes logging setup and ensures consistent logging behavior throughout the application.

renamer/logging_config.py

@@ -0,0 +1,46 @@
+"""Singleton logging configuration for the renamer application.
+
+This module provides centralized logging configuration that is initialized
+once and used throughout the application.
+"""
+
+import logging
+import os
+import threading
+
+
+class LoggerConfig:
+    """Singleton logger configuration."""
+
+    _instance = None
+    _lock = threading.Lock()
+    _initialized = False
+
+    def __new__(cls):
+        """Create or return singleton instance."""
+        if cls._instance is None:
+            with cls._lock:
+                if cls._instance is None:
+                    cls._instance = super().__new__(cls)
+        return cls._instance
+
+    def __init__(self):
+        """Initialize logging configuration (only once)."""
+        if LoggerConfig._initialized:
+            return
+
+        # Check environment variable for formatter logging
+        if os.getenv('FORMATTER_LOG', '0') == '1':
+            logging.basicConfig(
+                filename='formatter.log',
+                level=logging.DEBUG,
+                format='%(asctime)s - %(levelname)s - %(message)s'
+            )
+        else:
+            logging.basicConfig(level=logging.INFO)
+
+        LoggerConfig._initialized = True
+
+
+# Initialize logging on import
+LoggerConfig()