fix: address bot suggestions for stacklevel and redundant config initialization

Signed-off-by: Akshat Kumar <akshat230405@gmail.com>

Author: Akshat8510

src/google/adk/agents/llm_agent.py

@@ -875,7 +875,7 @@ def model_post_init(self, __context: Any) -> None:
           'planner with `thinking_config` are provided. The '
           "planner's configuration will take precedence.",
           UserWarning,
-          stacklevel=3,
+          stacklevel=5,
       )
 
   @classmethod

src/google/adk/planners/built_in_planner.py

@@ -61,7 +61,6 @@ def apply_thinking_config(self, llm_request: LlmRequest) -> None:
       llm_request: The LLM request to apply the thinking config to.
     """
     if self.thinking_config:
-      llm_request.config = llm_request.config or types.GenerateContentConfig()
       if llm_request.config.thinking_config:
         _LOGGER.info(
             'Overwriting `thinking_config` from `generate_content_config` with '

tests/unittests/agents/test_llm_agent_fields.py

@@ -19,9 +19,6 @@
 from typing import Optional
 from unittest import mock
 
-from pydantic import BaseModel
-import pytest
-
 from google.adk.agents.callback_context import CallbackContext
 from google.adk.agents.invocation_context import InvocationContext
 from google.adk.agents.llm_agent import LlmAgent
@@ -33,10 +30,12 @@
 from google.adk.models.registry import LLMRegistry
 from google.adk.planners.built_in_planner import BuiltInPlanner
 from google.adk.sessions.in_memory_session_service import InMemorySessionService
-from google.adk.tools.google_search_tool import GoogleSearchTool
 from google.adk.tools.google_search_tool import google_search
+from google.adk.tools.google_search_tool import GoogleSearchTool
 from google.adk.tools.vertex_ai_search_tool import VertexAiSearchTool
 from google.genai import types
+from pydantic import BaseModel
+import pytest
 
 
 async def _create_readonly_context(