Apply format kernel to helpers

[joshqsumner]

Describe your changes
Applies the _format_kernel function from #1943 to functions with a kernel in the _helpers module to allow more flexible kernel specification in closing, erode, and dilate.

Type of update
This is a feature enhancement.

Associated issues
Part of #1911

Additional context
Builds on changes from #1943

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]

DeepSource Code Review

We reviewed changes in 10eaa2c...c27913a on this pull request. Below is the summary for the review, and you can see the individual issues we found as inline review comments.

See full review on DeepSource ↗

PR Report Card

Overall Grade

Security   Reliability   Complexity   Hygiene   Coverage

Code Review Summary

Analyzer	Status	Updated (UTC)	Details
Python		Jun 8, 2026 6:08p.m.	Review ↗
Code coverage		Jun 8, 2026 6:08p.m.	Review ↗

Code Coverage Summary

Language	Line Coverage (New Code)	Line Coverage (Overall)
Aggregate	100% [✓ above threshold]	99.9% [▼ down 0.1% from main]
Python	100% [✓ above threshold]	99.9% [▼ down 0.1% from main]

➟ Additional coverage metrics may have been reported. See full coverage report ↗

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