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.

Start with the linked TypeScript SDK Options.toolAliases documentation, then trace how the Python SDK configures its built-in tools; the issue names no Python files or tests. Done means Python SDK users can replace built-in tools such as Read, Write, and Bash with custom tools.

Written by the indexing model from the issue text.