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

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

Section 5.6: variance triangle for normalized block fluctuations

This module re-exports the split files proving Lemma l.variance.estimate.quadratic.