Coordinate symmetry on centered cubes

Re-exports the original CoarseGraining coordinate geometry and Sobolev symmetry constructors from commit c7ddd76c08ade64fed1b8d2ca51be14dfee8deb4 (Apache-2.0). Geometry, H¹ transport, and H¹₀ approximation transport are separated while retaining all original namespaces, mathematical definitions, theorem statements, and proof bodies.