### Why is this Change Important & Necessary?
Partially addresses Submitty#12927 
Before, the download csv button would not populate the registration
subsections into the csv.
This was an issue since the download csv was not really compatible with
the rest of the page or the upload csv feature. (ie, if you changed some
subsections then later downloaded the csv, you would not see the
changes).

### What is the New Behavior?
The instructor can now see the subsection field populated in the CSV. 
<img width="2050" height="1166" alt="image"
src="https://github.com/user-attachments/assets/ea3402f8-17d3-4708-8516-c128351d1bce"
/>

### What steps should a reviewer take to reproduce or test the bug or
new feature?
0. verify the original functionality on main (downloading the csv does
not show the user subsections)
1. Go to the manage students page as instructor
2. make sure you have subsections set for some students
3. download the csv and observe that subsections are filled.
4. edit some data (including subsections) in the csv and re-upload, the
students should update accordingly.

### Automated Testing & Documentation
I am not sure if the upload CSV is documented by the Cypress e2e tests,
will investigate further.

### Other information
Not a breaking change.
No security concerns. 
I took this opportunity to refactor the download CSV a little bit to
make it easier to add / remove CSV header options in the future.

* main: (78 commits)
  [Bugfix:TAGrading] Auto-open single file (#12625)
  [Feature:InstructorUI] Add sortable columns to manage students (#12957)
  [Dependency] Bump php-ds/php-ds from 1.7.0 to 2.0.1 in /site (#12827)
  [Refactor:TAGrading] Events Infrastructure & StatusBanner (#12941)
  [Dependency] Bump sqlalchemy from 2.0.48 to 2.0.51 in /.setup/pip (#12884)
  [Bugfix:Developer] trust hashicorp for vagrant install (#12968)
  [Feature:TAGrading] Backend for submission clustering (#12886)
  [Bugfix:InstructorUI] Missing Subsection in the Edit User form (#12955)
  [Bugfix:Submission] Warning Banners Accessibility Fix (#12956)
  [Bugfix:System] Preserve signup fields (#12939)
  [Bugfix:InstructorUI] Fix Csv Download of Subsections (#12954)
  [Bugfix:InstructorUI] Fix Manage Students Toggle Columns (#12953)
  [Feature:TAGrading] Persistent Auto-Open (#12931)
  [Bugfix:Submission] Dot File Upload (#12924)
  [Refactor:System] Declutter workers (#12815)
  [Bugfix:Developer] save/restore autograding_containers.json (#12952)
  [Bugfix:InstructorUI] Create Course Validation (#12949)
  [Testing:Notifications] Fix grade_inquiries.spec.js (#12950)
  [UI/UX:System] Add fullscreen button vue component (#12936)
  [Bugfix:TAGrading] Student Name Resize (#12946)
  ...

# Conflicts:
#	.pylintrc