In-memory equivalent of PatientChartsRepo.getAllForPatient's since filter. Keeps a chart if:
PatientChartsRepo.getAllForPatient
since
external_document_created_at >= cutoff
external_document_created_at is null AND created_at >= cutoff
In-memory equivalent of
PatientChartsRepo.getAllForPatient'ssincefilter. Keeps a chart if:external_document_created_at >= cutoff, ORexternal_document_created_at is null AND created_at >= cutoff