Add Types

[bh2smith]

All libraries depending on this package are running into this mypy error:

error: Skipping analyzing "near_lake_framework": module is installed, but missing library stubs or py.typed marker  [import-untyped]
note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports

It should be as straightforward as adding this empty py.typed file and including it in the setup.py file.

Test Plan

1. Build the project locally python -m build.
2. Install the local build in a project that depends on it (e.g. https://github.com/near/gas-station-event-indexer) pip install -e ../near_lake_framework
3. Run mypy (see no more missing library stubs warnings)...

After step 1 you can also unzip the build and see that the py.typed file is included in the build.

Note that there were additional type errors (referenced in #10). If this is accepted this PR also closes #10.

I think we should also BUMP the required python version of this package to at least 3.8, but preferably >=3.9.

[frolvanya]

Thanks for your contribution! I'll test all your PRs soon and merge them