gh-37693: Implement the hypercenter and upper central series for finite dimensional Lie algebras
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We implement the upper central series and hypercenter of a finite
dimensional Lie algebra.
As part of the testing, we found improvements could be made to the
generic example (needed so the example would work with these tests): We
moved the `reduce()` method up to the category. Implemented methods
expected for the subalgebras. Better input verification. Elements are
now hashable. We had to work around the fact that `lift()` is serving
multiple roles as to the UEA and to the ambient space for a Lie
subalgebra. This functionality needs to be divided (I take full
responsibility for this bad design) by renaming `lift` to something for
the UEA map, but this is a significant change that should be done on a
followup PR.
We also fixed some bugs and improved efficiency with changing vectors
into Lie algebra elements.
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### :hourglass: Dependencies
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URL: https://github.com/sagemath/sage/pull/37693
Reported by: Travis Scrimshaw
Reviewer(s): Matthias Köppe, Travis Scrimshaw
