Test, fix, and simplify ATR parsing

Added
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* Add `ATR.py` test cases. Code coverage of `ATR.py` is now 100%.
* Add type annotations to everything in `ATR.py`.

Changed
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* `SmartcardException` will be raised if the ATR is less than 2 bytes.

Fixed
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* The ATR `checksumOK` attribute is now guaranteed to exist.
  If there is no checksum, `checksumOK` will be set to `None`.

  Previously, the attribute would only exist if a checksum existed.

* The checksum byte will now always be rendered if it exists.

  Previously, if the checksum byte was `0x00`, it would not be rendered.

Removed
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* Remove the `__main__` code in `ATR.py`.

  All of the ATRs are present in the test suite.

Deprecated
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* The ATR hasTA/hasTB/hasTC/hasTD attributes are deprecated.

  Users may compare items in the TA/TB/TC/TD attributes to `None`.

* The ATR `dump()` method is deprecated.

  Users may call the new `render()` method and print the result.