fix: add utf-8 encoding to file based reads and writes of eval data

This will help manage encoding consistency between reads and writes.

PiperOrigin-RevId: 784741646

Author: ankursharmas

src/google/adk/evaluation/local_eval_set_results_manager.py

@@ -60,7 +60,7 @@ def save_eval_set_result(
         eval_set_result.eval_set_result_name + _EVAL_SET_RESULT_FILE_EXTENSION,
     )
     logger.info("Writing eval result to file: %s", eval_set_result_file_path)
-    with open(eval_set_result_file_path, "w") as f:
+    with open(eval_set_result_file_path, "w", encoding="utf-8") as f:
       f.write(json.dumps(eval_set_result_json, indent=2))
 
   @override
@@ -78,7 +78,7 @@ def get_eval_set_result(
     )
     if not os.path.exists(maybe_eval_result_file_path):
       raise NotFoundError(f"Eval set result `{eval_set_result_id}` not found.")
-    with open(maybe_eval_result_file_path, "r") as file:
+    with open(maybe_eval_result_file_path, "r", encoding="utf-8") as file:
       eval_result_data = json.load(file)
     return EvalSetResult.model_validate_json(eval_result_data)
 

src/google/adk/evaluation/local_eval_sets_manager.py

@@ -315,7 +315,7 @@ def _validate_id(self, id_name: str, id_value: str):
       )
 
   def _write_eval_set_to_path(self, eval_set_path: str, eval_set: EvalSet):
-    with open(eval_set_path, "w") as f:
+    with open(eval_set_path, "w", encoding="utf-8") as f:
       f.write(eval_set.model_dump_json(indent=2))
 
   def _save_eval_set(self, app_name: str, eval_set_id: str, eval_set: EvalSet):