Coarse-graining support: Support.CoarseGraining.ResponseIdentities.AverageFormulas

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

ResponseIdentities average formulas (aggregate re-export)

Previously a 1758-line monolithic module; now split along thematic boundaries into the four files imported above. Shim for backward compatibility.