Include py.typed in packaging

[gadomski]

Related Issue(s):

• Supersedes #450
• Closes #444

Description:

Manually tested by running python -m build in a fresh venv and checking the created files:

$ python -m build >/dev/null 2>&1
$ tar -tvf dist/stactools-0.4.8.tar.gz | grep py.typed
-rw-r--r--  0 gadomski staff       0 Jun 30 08:34 stactools-0.4.8/src/stactools/cli/py.typed
-rw-r--r--  0 gadomski staff       0 Jun 30 08:34 stactools-0.4.8/src/stactools/core/py.typed
-rw-r--r--  0 gadomski staff       0 Jun 30 08:34 stactools-0.4.8/src/stactools/testing/py.typed
$ pip install dist/stactools-0.4.8-py3-none-any.whl >/dev/null
$ mypy -c "from stactools.core.io.xml import XmlElement"
Success: no issues found in 1 source file

PR checklist:

• [ ] Code is formatted (run scripts/format).
• [ ] Code lints properly (run scripts/lint).
• [ ] Tests pass (run scripts/test).
• [ ] Documentation has been updated to reflect changes, if applicable.
• [ ] Changes are added to the CHANGELOG.

[jsignell]

ah good call. Yeah this looks right