Add py.typed to the gsb package

[OpenBagTwo]

Summary

Implements #35

List of Changes

• Adds py.typed to the gsb package

Tech Debt and Other Concerns

Validation Performed

1. Created a clean virtual environment and installed gsb (version 0.0.2) via pip along with mypy.
2. Created the following python file, which has numerous type issues:

   from gsb import history
   x: tuple[str] = history.get_history(".", since="today")

3. Ran mypy on the python file and got back the following response:

   hint_test.py:1: error: Skipping analyzing "gsb": module is installed, but missing library stubs or py.typed marker  [import]
   hint_test.py:1: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports
   Found 1 error in 1 file (checked 1 source file)

4. Navigated to my project repo and ran pip install -e . (gsb -V now replies with "gsb, version 0.0.2+24.g4a1a6a6")
5. Ran mypy again. Got the response:

   hint_test.py:2: error: Incompatible types in assignment (expression has type "list[_Revision]", variable has type "tuple[str]")  [assignment]
   hint_test.py:2: error: Argument 1 to "get_history" has incompatible type "str"; expected "Path"  [arg-type]
   hint_test.py:2: error: Argument "since" to "get_history" has incompatible type "str"; expected "date"  [arg-type]
   Found 3 errors in 1 file (checked 1 source file)

PR Type

• [ ] This PR introduces a breaking change (will require a bump in the minor version)
• [ ] The changes in this PR are high urgency and necessitate a hotfix or patch release (will require rebasing off of release)
• [ ] This is a release (staging) PR (maintainer use only)

Checklist:

• [x] I have read the contributor's guide
• [x] I have run mkdocs serve locally and ensured that all API docs and changes I have made to the static pages are rendering correctly, with all links working
• [x] All tech debt concerns have been resolved, documented as issues, or otherwise accepted
• [x] I agree to license my contribution to this project under the GNU Public License v3