Add three decode-only CsvConfig options plus a codec convenience:

- comment: drop comment-prefixed lines, detected only at the start of a
  line so a marker inside a quoted or mid-field value stays content
- skipRows: skip leading rows before the header row (a preamble)
- maxRows: cap the returned data rows; the batch decoders stop early and
  the streaming decoder stops emitting
- CsvCodec.decodeToMaps: decode straight to header-keyed maps

All three options apply across every decode path (batch typed, strings,
flexible, the typed decoders, table, maps, and the streaming decoder) and
are held to identical output by the conformance suite, which splits input
at every chunk boundary. Closes the comment-skipping and row-windowing
roadmap items.