Add `py.typed` file to indicate package supports typing

[ortk95]

https://peps.python.org/pep-0561/#packaging-type-information

Pull request checklist

• [x] Add a clear description of the change
• [x] Add any new tests needed
• [x] Run spell check on new text visible to user (documentation, GUI etc.)
• [x] Check any changes to requirements.txt are reflected in setup.py and conda-forge feedstock
• [x] Check code passes CI checks (run run_ci.sh or check GitHub Actions)

See CONTRIBUTING.md for more details.

[coveralls]

Pull Request Test Coverage Report for Build 8189436190

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.573%

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Totals
Change from base Build 8084517656:	0.0%
Covered Lines:	2880
Relevant Lines:	2892

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💛 - Coveralls