Modernize packaging

[jqtrde]

This PR:

• Migrates packaging to pyproject.toml
• Loads the version from package metadata
• Drops support for versions < 3.10 and simplifies the CI matrix
• Fixes up the CLI packages a bit

Tested with the following:

# clean python venv
$ mkdir -p /tmp/tilesets-cli-test
$ cd /tmp/tilesets-cli-test
$ python -m venv .venv
$ source .venv/bin/activate
$ python -V
Python 3.10.19


# build tilesets-cli with 3.10
$ cd /src/tilesets-cli
$ python -m pip install --upgrade pip build
$ python -m build

# install build into clean venv
$ cd /tmp/tilesets-cli-test
$ python -m pip install /src/tilesets-cli/dist/*.whl

# verify entrypoint + import
$ tilesets --help
...help text

$ tilesets --version
1.15.0

$ python -c "import mapbox_tilesets.scripts.cli; print('ok')"
ok