Use quiz attempts for completion state

[aiko-gh]

Summary

• fetch quiz attempt data with mod_quiz_get_user_attempts during Moodle contents sync
• mark quizzes completed when the user has a non-preview attempt in finished state, falling back to module completion only when attempt data is unavailable
• add collector tests for finished, in-progress, and fallback quiz completion behavior

Live investigation

• core_course_get_contents returned completiondata.state = 0 for Thermo quizzes 100064 and 100067, which kept them incorrectly incomplete
• mod_quiz_get_user_attempts for those same quiz instance IDs returned one attempt each with state: "finished"
• other Thermo quizzes checked (100061, 100070, 100073, 100076, 100079, 100082, 100085, 100100) returned zero attempts

Verification

• PYTHONPATH=/tmp/moodle-tracker-codex-kjvtTb/src MOODLE_BASE_URL=https://example.invalid MOODLE_USERNAME=test MOODLE_PASSWORD=test pytest -q tests/test_collectors.py
• rebuilt and restarted live api and worker containers from /home/sam/projects/moodle-tracker
• ran POST /sync/run/moodle_contents against the live app
• confirmed /items/78 and /items/80 now return completion_state: completed
• confirmed those quizzes no longer appear in GET /risks

Notes

• the broader local suite still has two unrelated failures in tests/test_persistence_notifications.py around change classification (refresh_only / deadline_changed), not touched by this patch