Port from Mypy to `ty`

[johnthagen]

When ty, Astral's Python type checker, is out of preview-status, evaluate replacing Mypy with it.

• https://github.com/astral-sh/ty

Potential blocker

• Reimplement popular Mypy Plugins astral-sh/ty#291

[johnthagen]

Badge URL to use

[![ty](https://img.shields.io/endpoint?url=https://raw.githubusercontent.com/astral-sh/ty/main/assets/badge/v0.json)](https://github.com/astral-sh/ty)

[johnthagen]

0.0.2

This is the first Beta release of ty, which we're now ready to recommend to motivated users for
production use.

General release is getting closer.