py.typed file / type stubs are missing

Describe the bug
The polygon package does not export its type information to mypy, which causes mypy to fail when used on downstream packages

To Reproduce

1. Download examples/stocks-daily_open_close.py or any other example file
2. mypy stocks-daily_open_close.py
3. Observe the following error:

stocks-daily_open_close.py:1: error: Skipping analyzing "polygon": module is installed, but missing library stubs or py.typed marker  [import-untyped]
stocks-daily_open_close.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)

Expected behavior
The type checks should pass

Additional context
I think all that is needed is to add the missing py.typed file to the polygon package

まず、インストールされている polygon パッケージを見つけ、mypy を使って examples/stocks-daily_open_close.py で報告を再現します。Issue で説明されているとおりにパッケージが型情報をエクスポートしていることを確認し、その後、missing-stubs エラーなしで例が型チェックを通過することを確認します。