Improve Keep Redundant Spaces algorithm for PatchedPhaseDiagram

[CompRhys]

Summary

• modularize the keep redundant spaces code, and fix the algorithm which previously didn't get rid of all the redundant spaces.

Checklist

• Google format doc strings added. Check with ruff.
• Type annotations included. Check with mypy.
• Tests added for new features/fixes.
• If applicable, new classes/functions/modules have duecredit @due.dcite decorators to reference relevant papers by DOI (example)

[janosh]

PatchedPhaseDiagrams pickled to disk with this change should result in smaller files as fewer sub phase diagrams need to be stored

@CompRhys just corrected me, all this is saving are some memory IDs which are on the order of a few bytes so no meaningful decrease in file size expected

[mkhorton]

Thanks @CompRhys!

I think some comment strings need to be updated: for example, there is a claim that PatchedPhaseDiagram uses the same as_dict() as PhaseDiagram but this is not the case (computed_data, i.e. including the qhull entries, are not stored). Otherwise this looks great.

[janosh]

@CompRhys thanks for addressing the outdated doc strings!