Failure to list MCP tools due to unsupported `format`

### What happened?

**Describe the bug**

When trying to make use of the [Notion MCP server](https://github.com/makenotion/notion-mcp-server), I ran into the following exception when calling `autogen_ext.tools.mcp.mcp_server_tools`.

```
Exception has occurred: FormatNotSupportedError
Unknown format `json` for `icon` in `GeneratedModel`
  File "main.py", line 59, in main
    tools = await mcp_server_tools(server_params)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "main.py", line 66, in <module>
    asyncio.run(main())
autogen_core.utils._json_to_pydantic.FormatNotSupportedError: Unknown format `json` for `icon` in `GeneratedModel`
```

This seems to stem from their [use of](https://github.com/makenotion/notion-mcp-server/blob/f8355fd09e7da84228eff7edfe1864237ebf162c/scripts/notion-openapi.json#L1433-L1437) `"format": "json"` within the `inputSchema` on tool definitions. Whereas, `json` is not a [_known_/defined format](https://github.com/microsoft/autogen/blob/7c536a8c95b9600f7c30e08473148839ecaf57c7/python/packages/autogen-core/src/autogen_core/utils/_json_to_pydantic.py#L58-L85) value within the autogen utils for [converting json to pydantic](https://github.com/microsoft/autogen/blob/7c536a8c95b9600f7c30e08473148839ecaf57c7/python/packages/autogen-core/src/autogen_core/utils/_json_to_pydantic.py#L335).

Disclaimer: I'm a complete n00b to all of this, so I don't quite know where to turn or how best to address this issue. That being said... 

The MCP specification [defines](https://modelcontextprotocol.io/specification/2025-03-26/server/tools#tool):
> `inputSchema`: JSON Schema defining expected parameters

[JSON Schema](https://json-schema.org/understanding-json-schema/reference/type#built-in-formats), in turn, specifies:
> `format` is not limited to a specific set of valid values or types. Users may define their own custom keywords including ones that work with JSON data types other than `string`, such as `number`.

Hence, I wonder, should this code be as opinionated as it is right now, and fail for any unknown format? Alternatively, as a short-stop/quick-fix, would the maintainers be open to adding support for `"format": "json"`? Adding support for JSON is an easy fix, and I have [the code ready](https://github.com/microsoft/autogen/commit/79388b7aa1963db71c574c5b939660b6a2048f8a) to open up a PR; however, I am hesitating as the utils method `schema_to_pydantic_model` is used in other parts of the codebase beyond just converting tool schemas. 

**To Reproduce**
``` py
import asyncio
from autogen_ext.tools.mcp import StdioServerParams, mcp_server_tools

async def main() -> None:
    server_params = StdioServerParams(
        command="npx", args=["-y", "@notionhq/notion-mcp-server"]
    )

    # Get all available tools from the server
    tools = await mcp_server_tools(server_params)

    for tool in tools:
        print(f"{tool.name} - {tool.description}")


if __name__ == "__main__":
    asyncio.run(main())
```

**Expected behavior**

I would expect to be able to use _any_ (valid) MCP server with Autogen without any error.

### Which packages was the bug in?

Python Core (autogen-core), Python Extensions (autogen-ext)

### AutoGen library version.

Python dev (main branch)

### Other library version.

_No response_

### Model used

_No response_

### Model provider

None

### Other model provider

_No response_

### Python version

3.11

### .NET version

None

### Operating system

Ubuntu

Labels: needs-triage
State: closed