normalize_tool_arguments

Ensure arguments is always a proper JSON string with robust error handling.

Handles various malformed inputs from LLMs including:

• Valid JSON strings
• Python dict strings (e.g., "{'key': 'value'}")
• Multiple layers of JSON wrapping (e.g., '"{\"key\": \"value\"}"')
• Malformed outputs with trailing characters (e.g., '"{}""}')
• Unbalanced braces
• Empty or invalid inputs