feat: add authz permission for the course authoring list

[dwong2708]

Refactor course access listing to single-pass hybrid AuthZ + legacy approach

Summary

This PR refactors get_courses_accessible_to_user to improve performance, readability, and maintainability by introducing a single-pass hybrid access evaluation model.

Instead of splitting courses into separate AuthZ and legacy pipelines and merging results afterward, this implementation evaluates access per course in a single pass, then performs a single batched query to retrieve the final course list.

Key Improvements

Single-pass access evaluation

• Replaced the dual pipeline (AuthZ vs legacy) with a unified loop.
• Each course is evaluated once using:
  - user_has_course_permission(...)
• Eliminates duplicated logic and merging complexity.

Scoped full scan to staff users only

• Staff users still require evaluating all courses (expected behavior).
• Non-staff users now operate only on candidate course keys, avoiding unnecessary full table scans.

if is_staff_user:
    candidate_keys = CourseOverview.get_all_courses().values_list("id", flat=True)
else:
    candidate_keys = _get_candidate_course_keys(request)

Deferred object fetching

• Only fetch full CourseOverview objects after access filtering
• Reduces memory usage and DB overhead

Centralized filtering and ordering

• Filters (search, active/archived, ordering) are applied once at the end
• Ensures consistent behavior and avoids repeated processing

Improved readability and maintainability

• Clear step-based flow:

1. Determine candidate keys
2. Evaluate access
3. Batch fetch
4. Apply filters

• Reduced cognitive complexity and branching

Testing Notes

• Existing tests should continue to pass without modification
• Recommended additional coverage:
  • Mixed AuthZ + legacy access scenarios
  • Staff vs non-staff behavior
  • Empty access cases

Deadline

Verawood

Other information

Resolves: openedx/openedx-authz#190

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