[MNT] Fixes linting issues in base, networks, registry modules

[SamiAlavi]

Reference Issues/PRs

#4182

What does this implement/fix? Explain your changes.

• Fix B028 No explicit stacklevel keyword argument found

Does your contribution introduce a new dependency? If yes, which one?

No

What should a reviewer concentrate their feedback on?

• B028 No explicit stacklevel keyword argument found

Did you add any tests for the change?

No

Any other comments?

No

PR checklist

For all contributions

• I've added myself to the list of contributors.
• Optionally, I've updated sktime's CODEOWNERS to receive notifications about future changes to these files.
• The PR title starts with either [ENH], [MNT], [DOC], or [BUG] indicating whether the PR topic is related to enhancement, maintenance, documentation, or bug.

For new estimators

• I've added the estimator to the online documentation.
• I've updated the existing example notebooks or provided a new one to showcase how my estimator works.

[fkiraly]

Thanks a lot, the second!