FormalPolyhedraModule: support infinite bases

[mkoeppe]

... in particular the free modules

• generated by all polyhedra
• generated by all lower-dimensional polyhedra
• generated by all polyhedra with lines

Via #19448, all finitely generated formal polyhedra modules can be expressed as submodules.

[mkoeppe]

Wondering if I should expect that modules generated by subfamilies of some basis coerce into the module generated by the basis.

Or perhaps I should be constructing every module explicitly as a submodule of the ambient infinite-dimensional module?

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Last 10 new commits:

​fa0dd63	FormalPolyhedraModule: Add test for an infinite basis
​98dc756	Improvements to submodules.
​8006b8e	Merge branch 'public/categories/improve_submodules-19448' of trac.sagemath.org:sage into public/categories/improve_submodules-19448
​147583b	Merge branch 'public/categories/improve_submodules-19448' of git://trac.sagemath.org/sage into public/categories/improve_submodules-19448
​d4838df	Removing cmp for key.
​09f8caa	Merge branch 'public/categories/improve_submodules-19448' of git://trac.sagemath.org/sage into public/categories/improve_submodules-19448
​1267467	Fixing failures and allowing echelon_form to handle oo-dim modules.
​d8a1c50	Fixing doctests and making _vector_ and from_vector methods more consistent.
​cfc62e0	Merge branch 'public/categories/improve_submodules-19448' of git://trac.sagemath.org/sage into t/29812/formalpolyhedramodule_infinite_bases
​f6500b1	FormalPolyhedraModule: Add first infinite-dimensional examples

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​123f2ed

sage.geometry.polyhedra.facade_parent: New

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

[mkoeppe]

Setting new milestone based on a cursory review of ticket status, priority, and last modification date.