[MNT] resolve pre-commit issues on main

[yarnabrina]

Running pre-commit on main branch finds a few linting issues. These are probably introduced because of old PR's before adding the linters, or because of some skipped CI's. This PR attempts to solve these.

Steps followed:

1. Ran pre-commit run --all-files on main branch.
2. Got 3 issues regarding misisng module docstring, trailing whitespace and missing newline.
3. Fixed one by one.

[yarnabrina]

A related note is that most hook versions in .pre-commit-config.yaml is outdated. If updated to latest versions using pre-commit autoupdate, it leads to changes to ~140 files, and a lot of file blame will be modified. Skipped for now, but this may be worth considering in future.

[fkiraly]

Skipped for now, but this may be worth considering in future.

I would recommend, open an issue with the "maintenance" tag

[fkiraly]

Thanks!

odd that nothing complained when we merged these, some of these files were changed recently.