Support tool aliases similar to the TypeScript SDK's Options.toolAliases

It's often useful to be able to replace some of the built-in tools with your own tools, for instance to allow `Read` and `Write` to directly access some other file space or to dynamically customise `Bash` behaviour. The TypeScript Agent SDK allows this with the `toolAliases` in the [`Options`](https://code.claude.com/docs/en/agent-sdk/typescript#options). Please can the Python SDK be updated to support this functionality too?

I'd implement this myself and submit a PR, but I can't see how the TypeScript SDK implements this since it seems to be closed source.