Function buildChangeModel

Wraps an already-computed ManifestChangeReport (e.g. generateEnvArtifacts()'s internal evidenceChanges.report) in the Change Model's versioned shape, and correlates renames using the current run's renamedFrom declarations. currentContracts should be the same contracts the manifest was generated from (active contracts only, matching renderManifest()'s own scope -- same as every other input to this report family).