gh-35591: Implement twisted affine Lie algebras

    
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### 📚 Description

Untwisted affine Lie algebras have been implemented in Sage for some
time, but their twisted counterparts have been missing. They are more
complicated to implement due to the involvement of a diagram
automorphism, third roots of unity, and nonreduced root systems.

Along the way, I made some additional fixes in regards to this
enhancement:

- Brings coverage up to 100% in lie_algebras.
- Faster Killing matrix for Chevalley basis (which speeds up untwisted
affine brackets).
- Fix bug in creating the affine type from a finite type.

### 📝 Checklist

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- [x] I have created tests covering the changes.
- [x] I have updated the documentation accordingly.

### ⌛ Dependencies

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URL: #35591
Reported by: Travis Scrimshaw
Reviewer(s): Frédéric Chapoton