[Python]: Use rich tools

[gadenbuie]

Pairs with #65.

Requires shinychat for Python to support rich tool calling UI, which is now available in the dev version of shinychat that can be installed with

uv pip install git+https://github.com/posit-dev/shinychat.git

and requires chatlas >= 0.11.1

Rich tools in shinychat-python were added in posit-dev/shinychat#107