chore: Autoformat history_management agent codes

PiperOrigin-RevId: 785003632

Author: seanzhougoogle

contributing/samples/history_management/agent.py

@@ -66,11 +66,17 @@ async def check_prime(nums: list[int]) -> str:
 
 
 def create_slice_history_callback(n_recent_turns):
-  async def before_model_callback(callback_context: CallbackContext, llm_request: LlmRequest):
+  async def before_model_callback(
+      callback_context: CallbackContext, llm_request: LlmRequest
+  ):
     if n_recent_turns < 1:
       return
 
-    user_indexes = [i for i, content in enumerate(llm_request.contents) if content.role == "user"]
+    user_indexes = [
+        i
+        for i, content in enumerate(llm_request.contents)
+        if content.role == 'user'
+    ]
 
     if n_recent_turns > len(user_indexes):
       return