Adapt QQBar documentation

[lgoettgens]

Some more progress towards https://github.com/oscar-system/Oscar.jl/issues/3416.

This follows the approach of https://github.com/oscar-system/Oscar.jl/issues/3416#issuecomment-2047092266, i.e.:

• preparing for removal of CalciumQQBar (global constant)
• preparing for unexporting QQBar (global constant)
• adapt the documentation and tests to use algebraic_closure(QQ) instead.

In the next breaking release of Nemo, a few things marked with a TODO can be removed. This will only be a breaking change for Nemo, but not for Oscar.

[thofma]

Test failure looks real

[lgoettgens]

Test failure looks real

Some copy-and-paste error when adapting the tests probably. But needs to wait for me to get back to a computer

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 85.95%. Comparing base (3d975fd) to head (48dcd18).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1715   +/-   ##
=======================================
  Coverage   85.95%   85.95%           
=======================================
  Files          95       95           
  Lines       36503    36503           
=======================================
  Hits        31375    31375           
  Misses       5128     5128           

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[lgoettgens]

I think 5c8674d (#1715) together with the sentence that was already there is what you imagined @fingolfin ?

[lgoettgens]

Thanks @fingolfin for bringing this pr to this form. I am happy to have it merged