fix: add missing crop function to _DATA_FILE_HELPER_LIB

Fixes #4011

Author: osushinekotan

src/google/adk/flows/llm_flows/_code_execution.py

@@ -76,6 +76,10 @@ class DataFileUtil:
 _DATA_FILE_HELPER_LIB = '''
 import pandas as pd
 
+def crop(s: str, max_chars: int = 64) -> str:
+  """Crops a string to max_chars characters."""
+  return s[: max_chars - 3] + '...' if len(s) > max_chars else s
+
 def explore_df(df: pd.DataFrame) -> None:
   """Prints some information about a pandas DataFrame."""