fix: add py.typed marker for type-checking support

[AnujRewar]

Adds py.typed file to enable PEP 561 type hinting support

[coveralls]

Pull Request Test Coverage Report for Build 15752821764

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

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 88.517%

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Totals
Change from base Build 15688095219:	0.0%
Covered Lines:	1796
Relevant Lines:	2029

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💛 - Coveralls