Delta files and missing associated records

For GiveCampus constituent data and imports.

A follow-up file of changed constituents is not universally equivalent to a complete source file. The importer creates or updates mapped records, but cleanup can remove missing associated records in full and incremental imports. Some core constituent records are protected from this cleanup, but associated records may still be removed. Cleanup skips Salesforce and files smaller than half the largest previous processed non-test file size for the configuration/version family. That safeguard is not a contract that arbitrary partial uploads preserve all data. Confirm the record mappings/source contract and test before scheduling a changed-record-only feed.