feat: hydrate learner state for paginated assessment children

[santhosh-apphelix-2u]

Summary

Fixes CR-8239, where incrementally loaded assessment questions could appear unanswered even though the learner’s attempt state existed in StudentModule.

When the learner submitted the question again, the backend detected the existing attempt and returned:

The state of this problem has changed since you loaded this page.

Root cause

Lazy children were obtained through parent.get_children() and could already be bound to the parent’s shallow field-data cache. When the endpoint later supplied the correct batch cache, bind_for_student() skipped rebinding because the user ID was unchanged. As a result, the question rendered with default state instead of the learner’s persisted answer and attempt count.

Changes

• Resolve lazy children as fresh, unbound modulestore descriptors.
• Hydrate the learner state cache before binding and rendering children.
• Batch descendant state loading to avoid one state lookup per child.
• Preserve dynamic child selection, access checks, completion behavior, masquerading, and usage-key ordering.
• Display and retry individual lazy-load failures in the frontend.
• Add regression coverage for persisted problem state and batch cache population.