Handle QTI exercises

[rtibbles]

Ingest QTI assessment packages as individual QTI assessment items, rather than uploading a single opaque QTI zip.

Context

• Studio now accepts per-item QTI: each AssessmentItem is type='QTI' with a complete <qti-assessment-item> XML in raw_data, uploaded through the internal node-creation API ([QTI] Accept QTI items through the internal API for ricecooker import studio#6002).

The Change

• Parse a QTI/IMS content package: read its manifest, and extract each assessment item's XML and its referenced media.
• For each item, create a type='QTI' assessment item carrying the item XML in raw_data, with its media, through the internal node-creation API.

Acceptance Criteria

• A QTI package is ingested into individual type='QTI' assessment items, not a single zip file
• Each item's <qti-assessment-item> XML is uploaded in raw_data
• Referenced media is uploaded and linked to its item
• Studio accepts the upload via the internal API ([QTI] Accept QTI items through the internal API for ricecooker import studio#6002)

AI usage

Rewritten with Claude Code to match the per-item QTI ingestion model agreed in learningequality/studio#5998. The maintainer reviewed and approved the change.