Coarse-graining support: Support.Sobolev.Foundations.PoincareLpKernel

Imported from the Apache-2.0 CoarseGraining development at commit c7ddd76c08ade64fed1b8d2ca51be14dfee8deb4.

Riesz-kernel tools for convex-domain Poincare (aggregate re-export)

The contents of this file previously lived as one monolithic module; it has been split along section boundaries into the four modules imported above. This shim re-exports everything so downstream consumers keep working.