natives-parity.ss was a grab-bag (its own header called it 'parity'). Dissolve it
into homes that say what they hold:
- cat -> natives-transduce.ss (was natives-xform.ss, renamed for the
whole transducer surface: volatiles + cat + transduce/sequence)
- transient? -> transients.ss
- rseq -> natives-seq.ss
- hash family -> natives-misc.ss (the public hash API over jolt-hash)
The remainder — the #?() feature set, the reader-conditional + re-matcher tagged-map
ctors, and macroexpand — is a coherent reader/macro runtime-support unit, kept as
natives-reader.ss (np- prefix -> nr-). rt.ss loads + two comment refs updated.
Runtime .ss, no re-mint. make test green; hash/transient?/rseq/cat/macroexpand and
#?() reader features all verified.
