Remove isinstance check from FunctionTool (#3987) (#4056)

* Remove isinstance check from FunctionTool (#3987)

* Move __init__ Args to class docstring

---------

Co-authored-by: Eric Zhu <ekzhu@users.noreply.github.com>

python/packages/autogen-core/docs/src/user-guide/core-user-guide/framework/tools.ipynb

@@ -59,6 +59,13 @@
     "print(code_execution_tool.return_value_as_string(result))"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -82,6 +89,11 @@
     "To create a custom function tool, you just need to create a Python function\n",
     "and use the {py:class}`~autogen_core.components.tools.FunctionTool` class to wrap it.\n",
     "\n",
+    "The {py:class}`~autogen_core.components.tools.FunctionTool` class uses descriptions and type annotations\n",
+    "to inform the LLM when and how to use a given function. The description provides context\n",
+    "about the function’s purpose and intended use cases, while type annotations inform the LLM about\n",
+    "the expected parameters and return type.\n",
+    "\n",
     "For example, a simple tool to obtain the stock price of a company might look like this:"
    ]
   },
@@ -296,7 +308,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.11.9"
+   "version": "3.12.7"
   }
  },
  "nbformat": 4,