Re #7878. Fix memory leaks in Absorption algorithms

Also don't use pointers/new's unnecessarily.
Re #7878. Fix memory leaks in tests.
Re #7878. Fix memory leaks in Crystal package.

More of the same leaks of Material & NeutronAtom.
Re #7878. Fix leak of Material object.

Also remove test for null-ness of Material object as inspection shows
that can never be the case.
Re #7878. Remove no longer needed delete.
Merge remote branch 'origin/feature/7878_material_memory_leaks'