One list of the user as a CSV or Parquet file

Every record of one list in [start, end), as one file streamed in a single response (Content-Disposition: attachment). The columns are the members of the list's JSON records, in the same order and with the same names and values: times in UTC, a missing value empty (CSV) or null (Parquet), metadata (and the daily sources) as JSON text. ecg holds the recordings' metadata, not their voltage samples (in the archive and the FHIR Observation). samples holds every quantity type unless type names one. The file is not paged: cursor and limit are a 400. A failure once the file has started cuts the connection, so a truncated file never looks complete. See docs/exports.md.