test(progress-tracker): add course archiving edge case tests

[lmduy2612]

Description

Fixes #637

Adds comprehensive unit tests covering edge cases for course archiving in the progress-tracker contract:

1. test_archive_already_archived_course_panics: Verifies that attempting to archive an already-archived course panics with "course already archived".
2. test_enrolling_in_archived_course_panics: Verifies that attempting to enroll in an archived course panics with "course is archived".
3. test_completing_modules_in_archived_course_succeeds: Verifies that previously enrolled learners can still complete modules and record progress even after the course is archived.
4. test_submitting_quiz_scores_in_archived_course_succeeds: Verifies that previously enrolled learners can still submit quiz scores in an archived course.
5. test_archive_course_emits_course_archived_event: Verifies that archive_course publishes the expected (course_archived,) event with the course ID payload.

Testing

• Verified with cargo test --test progress_tests archived: All 5 tests pass without regressions.
• Code formatted with rustfmt.