Improved pyproject.toml

[Debilski]

Entry scripts need a build system to properly work, so I added hatchling. This allows us also to take the version from grader/__init__.py. I also removed the git revision stuff; not sure if this is really needed anymore.

Also added a dev dependency group so now grader+pytest works with uv without any manual venv:

git clone https://github.com/ASPP/grader
cd grader/

uv run pytest
uv run grader tests/data/year99/applications.csv