Lean on hatch-vcs for managing the package version

[kgaughan]

Not sure how interested you are in this, but I figure I'd might as well check.

This simplifies the mechanics of the release build a tad and means pyproject.toml doesn't need to be updated. It also means that __version__ is now a lot cheaper to determine as _version.py will be automatically generated with the correct information at build time.

Here's an example of triggering the build with uv build after creating the tag v1.2.0:

$ uv build
Building source distribution...
Building wheel from source distribution...
Successfully built dist/sqlit_tui-1.2.0.tar.gz
Successfully built dist/sqlit_tui-1.2.0-py3-none-any.whl

And the same with build:

$ uv run python -m build
      Built sqlit-tui @ file:///home/keith/projects/sqlit
Uninstalled 1 package in 0.56ms
Installed 1 package in 1ms
* Creating isolated environment: virtualenv+pip...
* Installing packages in isolated environment:
  - hatch-vcs
  - hatchling
* Getting build dependencies for sdist...
* Building sdist...
* Building wheel from sdist
* Creating isolated environment: virtualenv+pip...
* Installing packages in isolated environment:
  - hatch-vcs
  - hatchling
* Getting build dependencies for wheel...
* Building wheel...
Successfully built sqlit_tui-1.2.0.tar.gz and sqlit_tui-1.2.0-py3-none-any.whl

There should be no behavioural changes from how things currently work.

[Maxteabag]

Thanks for the PR!