docs(memory): use public preload_memory tool API in examples

docs/sessions/memory.md

@@ -357,13 +357,13 @@ When a memory service is configured, your agent can use a tool or callback to re
 === "Python"
     ```python
     from google.adk.agents import Agent
-    from google.adk.tools.preload_memory_tool import PreloadMemoryTool
+    from google.adk.tools import preload_memory
 
     agent = Agent(
         model=MODEL_ID,
         name='weather_sentiment_agent',
         instruction="...",
-        tools=[PreloadMemoryTool()]
+        tools=[preload_memory]
     )
     ```
 
@@ -418,7 +418,7 @@ To extract memories from your session, you need to call `add_session_to_memory`.
 === "Python"
     ```python
     from google.adk.agents import Agent
-    from google import adk
+    from google.adk.tools import preload_memory
 
     async def auto_save_session_to_memory_callback(callback_context):
         await callback_context.add_session_to_memory()
@@ -427,7 +427,7 @@ To extract memories from your session, you need to call `add_session_to_memory`.
         model=MODEL,
         name="Generic_QA_Agent",
         instruction="Answer the user's questions",
-        tools=[adk.tools.preload_memory_tool.PreloadMemoryTool()],
+        tools=[preload_memory],
         after_agent_callback=auto_save_session_to_memory_callback,
     )
     ```

examples/python/notebooks/express-mode-weather-agent.ipynb

@@ -65,7 +65,7 @@
     "# @title Import necessary libraries\n",
     "import os\n",
     "import asyncio\n",
-    "from google import adk\n",
+    "from google.adk.tools import preload_memory\n",
     "from google.adk.agents import Agent\n",
     "from google.adk.sessions import VertexAiSessionService\n",
     "from google.adk.memory import VertexAiMemoryBankService\n",
@@ -268,7 +268,7 @@
     "    \"You can help the user find what city has better weather based on their preferences using the preload memory tool.\",\n",
     "    tools=[\n",
     "        get_weather,\n",
-    "        adk.tools.preload_memory_tool.PreloadMemoryTool(),\n",
+    "        preload_memory,\n",
     "    ],  # Pass the function directly\n",
     ")\n",
     "\n",