readStampedLogArtifact

Read a stamped NDJSON artifact from source: the inverse of writeStampedLogArtifact, returning the StampedLogRecords in file order. Reads to end-of-source a line at a time, so a consumer merging across devices decodes each *.ndjson back without touching StampedLogRecord.serializer directly.

Reading is the caller's boundary to own the file/connection lifecycle — the source is drained but not closed.