data.priority-map: deftype interop fixes (rseq, arity-overload, empty, Sorted)

data.priority-map's whole suite passes (4/4). It leans on deftype/collection
interop jolt got wrong; four general fixes:

- rseq dispatches to a deftype's clojure.lang.Reversible.rseq method instead of
  always demanding a vector/sorted-coll (natives-seq.ss).
- a deftype method declared at two arities from two interfaces now dispatches by
  arity: the priority-map has seq[this] (Seqable) and seq[this ascending]
  (Sorted), so (.seq pm false) must reach the 2-arg one. find-method-any-protocol
  now matches the call's arg count via procedure-arity-mask, and a deftype's own
  declared method wins over the generic collection interop in dot-forms.
- (empty x) on a deftype/record with its own empty method uses it rather than
  returning {} (jolt.host/jrec-method? gate in clojure.core/empty).
- clojure.lang.Sorted (comparator / entryKey / seqFrom) works on jolt's
  sorted-map/set, so subseq/rsubseq run — including the priority-map delegating
  .comparator to its backing sorted-map (dot-forms.ss + host-static.ss).

Listed in docs/libraries.md + the site. One re-mint (clojure.core/empty);
everything else runtime. make test green (0 new divergences), shakesmoke
byte-identical.

jolt-core/clojure/core/22-coll.clj

@@ -133,6 +133,9 @@
 (defn empty [coll]
   (cond
     (nil? coll) nil
+    ;; a deftype/record with its own empty (IPersistentCollection) — e.g.
+    ;; data.priority-map — uses it, before the generic map/set/vector arms.
+    (jolt.host/jrec-method? coll "empty") (.empty coll)
     (sorted? coll) ((get (jolt.host/ref-get coll :ops) :empty) coll)
     (map? coll) (with-meta {} (meta coll))
     (set? coll) (with-meta #{} (meta coll))