Improve sorting of exercises when adding to assignment via book browse

[oscarlevin]

Currently if an instructor tries to add exercises to an assignment by browsing problems in the book, when navigating to a section, they get the exercises sorted by exercise name, which might be something like "Exercise 1.3.2" or "Exercise 1.3.11". But these are sorted as strings, so the 11th exercise appears before then 2nd.

This pr fixes that by adding a natural sort key function that sorts them "correctly"

[Copilot]

Pull request overview

This PR fixes incorrect lexicographic ordering of exercise identifiers when instructors browse book sections to add exercises to an assignment, by introducing a natural-sort key and re-sorting questions per subchapter after the DB query.

Changes:

• Added a _natural_sort_key helper to compare numeric runs numerically (e.g., 3.2.1 before 3.10.1).
• Re-sorted each subchapter’s question list in Python using the natural sort key to override DB string ordering.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (1)

components/rsptx/db/crud/question.py:837

• This introduces new ordering logic for chapter/subchapter question lists but there’s no regression test covering the natural sort behavior (e.g., ensuring "Exercise 1.3.2" sorts before "Exercise 1.3.11"). Since this endpoint drives assignment creation UI, adding a focused test would help prevent future regressions.

        for chapter_questions in questions.values():
            for subchapter_questions in chapter_questions.values():
                subchapter_questions.sort(
                    key=lambda q: _natural_sort_key(q.qnumber or q.name)
                )