Coarse-graining support: Support.Book.Ch05.Theorems.Section53.Common

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

Section 5.3 common imports

Shared base context for the split Section 5.3 files. The mathematical content lives in the three manuscript-lemma modules and their proof subdirectories.