Size scaling implementation in analysis functions

[HaleySchuhl]

Describe your changes
Size helper implementation in all linear & area type traits from analysis functions, also added to documentation.

Type of update
Is this a:

• New feature or feature enhancement

Associated issues

• Add optional pixel to mm conversion in plantcv.analyze.size and others #1649

Additional context
Scales area and linear measurements from pixels to real world measurements (e.g. millimeter) using the parameters pcv.params.px_width and pcv.params.px_height, where these parameters are the real world measurement per pixel.

For the reviewer
See this page for instructions on how to review the pull request.

• PR functionality reviewed in a Jupyter Notebook
• All tests pass
• Test coverage remains 100%
• Documentation tested
• New documentation pages added to plantcv/mkdocs.yml
• Changes to function input/output signatures added to updating.md
• Code reviewed
• PR approved

[deepsource-io]

Here's the code health analysis summary for commits 0961c3b..0f9751b. View details on DeepSource ↗.

Analysis Summary

Analyzer	Status	Summary	Link
Python	✅ Success		View Check ↗
Test coverage	✅ Success		View Check ↗

Code Coverage Report

Metric	Aggregate	Python
Branch Coverage	100%	100%
Composite Coverage	100%	100%
Line Coverage	100%	100%
New Branch Coverage	100%	100%
New Composite Coverage	100%	100%
New Line Coverage	100%, ✅ Above Threshold	100%, ✅ Above Threshold

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