sagemathgh-35884: `sage.{modular,schemes}`: Modularization fixes for imports; update `sage -fiximports`, add relint pattern 
    
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- Part of: sagemath#29705
- Cherry-picked from: sagemath#35095

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### ⌛ Dependencies

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- Depends on sagemath#35974 (to soothe the linter)

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URL: sagemath#35884
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee, Matthias Köppe

sagemathgh-35884: `sage.{modular,schemes}`: Modularization fixes for imports; update `sage -fiximports`, add relint pattern 
    
<!-- Please provide a concise, informative and self-explanatory title.
-->
<!-- Don't put issue numbers in the title. Put it in the Description
below. -->
<!-- For example, instead of "Fixes sagemath#12345", use "Add a new method to
multiply two integers" -->

### 📚 Description

<!-- Describe your changes here in detail. -->
<!-- Why is this change required? What problem does it solve? -->
<!-- If this PR resolves an open issue, please link to it here. For
example "Fixes sagemath#12345". -->

- Part of: sagemath#29705
- Cherry-picked from: sagemath#35095

<!-- If your change requires a documentation PR, please link it
appropriately. -->

### 📝 Checklist

<!-- Put an `x` in all the boxes that apply. It should be `[x]` not `[x
]`. -->

- [x] The title is concise, informative, and self-explanatory.
- [ ] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation accordingly.

### ⌛ Dependencies

<!-- List all open PRs that this PR logically depends on
- sagemath#12345: short description why this is a dependency
- sagemath#34567: ...
-->
- Depends on sagemath#35974 (to soothe the linter)

<!-- If you're unsure about any of these, don't hesitate to ask. We're
here to help! -->
    
URL: sagemath#35884
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee, Matthias Köppe