make script_id required in teacher_feedbacks

[davidsbailey]

Finishes PLAT-684. See migrating teacher feedback ids for more context.

Previous PRs:

• set script_id when creating teacher feedback #38553 makes sure the script_id field is always set when creating new TeacherFeedback objects
• Backfill script_id column in teacher_feedbacks table #38567 contains a backfill script which will be run in production before this migration is shipped

This PR contains a migration which does the following:

1. backfills data in non-production environments
2. marks the script_id column as non-null
3. adds validations to ensure script_id is present and equal to script_level.script_id
4. fixes unit tests to meet new constraints

Testing story

Ran the migration forward and backward locally, which succeeds even when some TeacherFeedbacks have no script_id.

Reviewer Checklist:

• Tests provide adequate coverage
• Privacy and Security impacts have been assessed
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Pull Request is labeled appropriately
• Follow-up work items (including potential tech debt) are tracked and linked

[davidsbailey]

only do this on create, because we want update to succeed at

code-dot-org/dashboard/app/models/teacher_feedback.rb

Line 83 in 4b0b0c0

def increment_visit_count

even if the script_level_id has become invalid.

[davidsbailey]

If anyone hits an error in this step in their local environment because some TeacherFeedback objects do not have script ids, they can resolve it by removing those TeacherFeedback objects.