Improve Linter Checks

[ayushr2]

Following up from illinois-cs241/broadway-api#58, some warnings like shadowing variable names, type mismatch warning slip by flake8. We should be able to catch such things and not let them slip into production code.

Maybe change the linter? But have been unsuccessful in finding linters which can do this.

[nmagerko]

Shadowing variable names should actually be caught by flake8. What you're referencing is using something like the variable name id which covers up the id builtin (which I think most linters probably don't care about, even though they probably should).

[ayushr2]

I think flake8 missed this one at least
https://github.com/illinois-cs241/broadway-api/pull/58/files#diff-6eef5733ba2a781f06839a31d0a6f5eeL153
https://github.com/illinois-cs241/broadway-api/pull/58/files#diff-6eef5733ba2a781f06839a31d0a6f5eeL164