Adding some rounding and error messaging for subplots

[stephenpardy]

Code PR

• I have read through the contributing notes and understand the structure of the package. In particular, if my PR modifies code of plotly.graph_objects, my modifications concern the codegen files and not generated files.
• I have added tests (if submitting a new feature or correcting a bug) or
  modified existing tests.
• For a new feature, I have added documentation examples in an existing or
  new tutorial notebook (please see the doc checklist as well).
• I have added a CHANGELOG entry if fixing/changing/adding anything substantial.
• For a new feature or a change in behaviour, I have updated the relevant docstrings in the code to describe the feature or behaviour (please see the doc checklist as well).

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[stephenpardy]

@AaronStiff - this is the PR to close #4124 - I mostly moved over your code here. I am seeing an NPM error in the CI/CD process though. Would you be available to review?

[AaronStiff]

@stephenpardy Great! I'm not really familiar with/involved in the build process though, but maybe @nicolaskruchten you could take a look? It would appear several other PRs are failing with the same issue.

[nicolaskruchten]

@alexcjohnson can you review this one plz? I'm not really available for the next few days

[stephenpardy]

@AaronStiff, @nicolaskruchten, or @alexcjohnson - just want to give this a gentle nudge to see if anyone is able to review and/or discuss the NPM build failure - I see that it is still around in some other PRs as well. Thank you.

[alexcjohnson]

Thanks @stephenpardy - we did some other work in the last few days to fix build/CI issues so with any luck the tests will pass now that I updated the branch. Would you be able to add a test of the problem you're fixing, as well as an entry in the changelog?

[alexcjohnson]

💃 Beautiful, thank you!