Revise docs and tests for group* functions

[milesfrain]

Description of the change

Intended to be merged following #191

This changes some of the tests, examples, and other docs for consistency, comparability, and to highlight some subtle differences in how the grouped results are sorted.

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Checklist:

• [x] Added the change to the changelog's "Unreleased" section with a reference to this PR (e.g. "- Made a change (#0000)")
• [x] Linked any existing issues or proposals that this pull request should close
• [x] Updated or added relevant documentation
• [x] Added a test for the contribution (if applicable)