Add function to print warning exactly once

Author: asogaard

src/graphnet/utilities/logging.py

@@ -1,6 +1,7 @@
 """Consistent and configurable logging across the project."""
 
 from collections import Counter
+from functools import lru_cache
 import re
 from typing import Optional
 import colorlog
@@ -53,6 +54,12 @@ def get_formatters() -> Tuple[logging.Formatter, colorlog.ColoredFormatter]:
     return basic_formatter, colored_formatter
 
 
+@lru_cache(1)
+def warn_once(logger: logging.Logger, message: str):
+    """Print `message` as warning exactly once."""
+    logger.warn(message)
+
+
 class RepeatFilter(object):
     """Filter out repeat messages."""