type annotation for exc.py

[enadeau]

Description

More work related to #373. This took it easy and did the exception file.

Type of change

Select the statement best describes this pull request.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• This is a documentation update
• Other (please describe)

Does your PR include tests

If you are fixing a bug or adding a feature, we appreciate (but do not require)
tests to support whatever fix of feature you're implementing.

• Yes
• No, i'd like some help with tests
• This change doesn't require tests

Did you include your contribution to the change log?

• Yes, changelog.md is up-to-date.

If you are having a hard time getting the tests to run correctly feel free to
ping one of the maintainers here!

[lwasser]

I see no issues with this pr!! approved ✨

[lwasser]

@enadeau thank you again for this!!