MNT: Clean up some style exceptions

[QuLogic]

PR summary

In these cases, a very small percentage of a file really needs an exception, so we can either add a noqa comment, or fix the style issue directly.

In files like pyplot.py, the file-level exception was obscuring that imports like re were unused, or that typing.cast was imported twice.

PR checklist

• [n/a] "closes #0000" is in the body of the PR description to link the related issue
• new and changed code is tested
• [n/a] Plotting related features are demonstrated in an example
• [n/a] New Features and API Changes are noted with a directive and release note
• [n/a] Documentation complies with general and docstring guidelines

[timhoffm]

While we‘ve said some time ago, that we don’t want to litter the code with noqa comments, I think it makes sense for some special cases. The alternative of globally applying the exception to a file is too coarse and can hide errors.