Replace `setuptools` backend with `uv`

[cthoyt]

uv is developing a build backend that will likely be able to replace setuptools.

• Tracking issue: Add a uv build backend astral-sh/uv#3957
• Initial release: Build basic source distributions astral-sh/uv#8886
• Documentation updates: Add docs for the uv build backend astral-sh/uv#7976
• Testing for my project: Switch to uv backend semantic-pydantic#3