Various Cython fixes to IndexedFreeModuleElement

[jdemeyer]

1. __div__ = __truediv__ is a bad idea for extension types because it acts on the Python method level and not on the slot level:

sage: F = CombinatorialFreeModule(QQ, [1,2,3]); B = F.basis(); f = 2*B[2] + 4*B[3]
sage: op = operator.truediv; timeit('op(f, 2)', repeat=100000, number=20)
20 loops, best of 100000: 4.99 µs per loop
sage: op = operator.div; timeit('op(f, 2)', repeat=100000, number=20)
20 loops, best of 100000: 5.45 µs per loop

2. IndexedFreeModuleElement and LieAlgebraElement implement arithmetic methods as cdef _add_ while every other class in Sage uses cpdef _add_.

3. six is slow and should be avoided.

4. IndexedFreeModuleElement must inherit from ModuleElement. This is because it uses the cpdef _lmul_ and cpdef _rmul_ which are provided by ModuleElement but not by Element. This causes trouble for FreeAlgebraElement which inherits from IndexedFreeModuleElement and AlgebraElement.

CC: @tscrim @nthiery

Component: cython

Author: Jeroen Demeyer

Branch/Commit: 8120246

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/23440

[jdemeyer]

Branch: u/jdemeyer/various_cython_fixes_to_indexedfreemoduleelement

[jdemeyer]

New commits:

8120246

Various Cython fixes

[jdemeyer]

Commit: 8120246

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:5

LGTM. Thank you for cleaning it up. The last part is also useful for #22591 (although I think there is more of a shortcomming of *ModuleAction in play, but this works around the problem).

[vbraun]

Changed branch from u/jdemeyer/various_cython_fixes_to_indexedfreemoduleelement to 8120246