Coarse-graining support: Support.Book.Ch05.Theorems.Section56.SmallContrastJBound

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

Section 5.6: small-contrast coarse-fluctuation iteration

This module re-exports the split proof of l.small.contrast.Jbound.