gh-37831: `FreeModuleHomset`: Create subclass `FreeModuleEndset`, add element methods for invariants `det`, `charpoly`, `fcp`, etc.
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We create
- a parent subclass `FreeModuleEndset` (of `FreeModuleHomset`)
- an element subclass `FiniteRankFreeModuleEndomorphism` (of
`FiniteRankFreeModuleMorphism`)
for the purpose of providing specific methods of endomorphisms, namely
the endomorphism invariants `det`, `trace`, `charpoly`, etc.
This is parallel to what is done
- for ModulesWithBasis in #37731
- in #37826
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preview.
### :hourglass: Dependencies
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URL: https://github.com/sagemath/sage/pull/37831
Reported by: Matthias Köppe
Reviewer(s): Eric Gourgoulhon, Travis Scrimshaw
