fix: update zero_to_hero package and README (#2578)

# What does this PR do?
<!-- Provide a short summary of what this PR does and why. Link to
relevant issues if applicable. -->
- update REAMDE.md format and python version
- update package name: CustomTool was renamed to ClientTool in
https://github.com/meta-llama/llama-stack-client-python/pull/73


<!-- If resolving an issue, uncomment and update the line below -->
Closes #2556 

## Test Plan
<!-- Describe the tests you ran to verify your changes with result
summaries. *Provide clear instructions so the plan can be easily
re-executed.* -->

Signed-off-by: Wen Zhou <wenzhou@redhat.com>

docs/zero_to_hero_guide/04_Tool_Calling101.ipynb

@@ -36,7 +36,7 @@
         "from dotenv import load_dotenv\n",
         "from llama_stack_client import LlamaStackClient\n",
         "from llama_stack_client.lib.agents.agent import Agent\n",
-        "from llama_stack_client.lib.agents.custom_tool import CustomTool\n",
+        "from llama_stack_client.lib.agents.client_tool import ClientTool\n",
         "from llama_stack_client.lib.agents.event_logger import EventLogger\n",
         "from llama_stack_client.types import CompletionMessage\n",
         "from llama_stack_client.types.agent_create_params import AgentConfig\n",
@@ -129,7 +129,7 @@
       "source": [
         "## Step 3: Create a Custom Tool Class\n",
         "\n",
-        "Here, we defines the `WebSearchTool` class, which extends `CustomTool` to integrate the Brave Search API with Llama Stack, enabling web search capabilities within AI workflows. The class handles incoming user queries, interacts with the `BraveSearch` class for data retrieval, and formats results for effective response generation."
+        "Here, we defines the `WebSearchTool` class, which extends `ClientTool` to integrate the Brave Search API with Llama Stack, enabling web search capabilities within AI workflows. The class handles incoming user queries, interacts with the `BraveSearch` class for data retrieval, and formats results for effective response generation."
       ]
     },
     {
@@ -139,7 +139,7 @@
       "metadata": {},
       "outputs": [],
       "source": [
-        "class WebSearchTool(CustomTool):\n",
+        "class WebSearchTool(ClientTool):\n",
         "    def __init__(self, api_key: str):\n",
         "        self.api_key = api_key\n",
         "        self.engine = BraveSearch(api_key)\n",