Move account create and update endpoints to RTKQ

[mwtrew]

Creates new RTKQ endpoints for user creation and updates. This replaces the createUser and updateUser async thunks. Most of the logic from there has been moved into the onQueryStarted lifecycle method of their respective
queries. The email change confirmation logic was moved out of there and into the My Account component, seeing as that's the only place it is used.

Components that used createUser/updateUser now use the generated RTKQ hook instead, and use its error handling instead of generalErrors. I have also added ExigentErrors to surface these where needed.

This affects a few different flows:

• Registration
• Updating details via My Account
• Updating details via Required Account Information or User Context Reconfirmation modals
• Consenting to LLM question usage

Registration and LLM questions have E2E test coverage. If the reviewer feels strongly about adding automated tests for the update flows we can do that, and that is probably sensible, but we don't currently have much in those areas so it would be a non-trivial amount of effort. Short of that I have manually tested thoroughly.

[codecov]

Codecov Report

❌ Patch coverage is 30.63063% with 77 lines in your changes missing coverage. Please review.
✅ Project coverage is 41.69%. Comparing base (19a2d80) to head (69f3889).
⚠️ Report is 17 commits behind head on main.

Files with missing lines	Patch %	Lines
src/app/state/slices/api/userApi.ts	11.11%	32 Missing ⚠️
...pp/components/elements/modals/EmailChangeModal.tsx	37.50%	10 Missing ⚠️
src/app/components/pages/MyAccount.tsx	35.71%	9 Missing ⚠️
...lements/modals/RequiredAccountInformationModal.tsx	22.22%	7 Missing ⚠️
...elements/modals/UserContextReconfirmationModal.tsx	64.28%	5 Missing ⚠️
...rc/app/components/pages/RegistrationSetDetails.tsx	44.44%	5 Missing ⚠️
...nents/navigation/LLMFreeTextQuestionInfoBanner.tsx	20.00%	4 Missing ⚠️
...pp/components/pages/RegistrationSetPreferences.tsx	33.33%	4 Missing ⚠️
src/IsaacAppTypes.tsx	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1816      +/-   ##
==========================================
+ Coverage   41.67%   41.69%   +0.01%     
==========================================
  Files         543      544       +1     
  Lines       23829    23835       +6     
  Branches     7867     7894      +27     
==========================================
+ Hits         9930     9937       +7     
- Misses      13255    13855     +600     
+ Partials      644       43     -601     

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[axlewin]

LGTM, this all works well.

In terms of automated tests for the update flows: considering the time it would take to add them (in addition to the time already spent manually verifying everything works), my suggestion would be that it's not worth blocking these changes on. @barna-isaac might feel more strongly about this, though?

[barna-isaac]

@axlewin: thanks for asking <3. I'd love to increase test coverage, but I certainly wouldn't block merging over this.