Fix marker validator with cycler (allow mix of classes)

[faisal-fawad]

PR summary

Closes #27596. Added basic support for combination of strings and integers to satisfy expected behavior.

PR checklist

• "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

[story645]

awesome, can you please add a test?

[github-actions]

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[ksunden]

Please add the following to the rcsetup.pyi file (Should be in roughly the same order as the .py file):

def validate_marker(s: Any) -> int | string: ...
def validate_markerlist(s: Any) -> list[int | string]: ...

[ksunden]

test failures unrelated

[story645]

@faisal-fawad we typically prefer changes be squashed down to a few commits - would you have interest in squashing down to 1 commit or would you like us to do so?

[faisal-fawad]

@story645 If you could handle it for this PR that would be preferred.

If you don't mind me asking, how could I squash the commits myself for future PRs?

[story645]

https://matplotlib.org/devdocs/devel/development_workflow.html#rewrite-commit-history

[QuLogic]

There are a few extra changes here; make sure you use a force push after rebasing.

[QuLogic]

Thanks @faisal-fawad! Congratulations on your first PR to Matplotlib 🎉 We hope to hear from you again.