core: close surfaced gaps — first-class sorted colls, with-out-str, rand arity, deref reduced

jolt-ti9: sorted-map/sorted-set are now first-class across the collection fns —
get/assoc/dissoc/conj/contains?/keys/vals/disj and call-as-fn all operate on the
wrapper and preserve sort order. The by-comparator constructors (sorted-map-by/
sorted-set-by) now thread the user comparator (numeric or boolean-predicate) through
all derived colls. Sorted predicates/ctors/ops moved above core-conj so the
collection fns can branch on them; jolt-invoke (interpreter) gets inline branches.

jolt-rfw: add with-out-str (binds output to a string buffer) + the macro.
jolt-ek3: (rand n) arity and deref-of-reduced (uuid? still deferred).

Specs: new io-spec.janet; sorted-spec expanded to pin the now-working map/set ops
and by-comparator ordering; predicate/number spec restorations.

test/spec/predicates-spec.janet

@@ -124,6 +124,7 @@
   ["integer? fraction" "false"  "(integer? 5.5)"]
   ["reduced? wrapped"  "true"   "(reduced? (reduced 1))"]
   ["reduced? plain"    "false"  "(reduced? 1)"]
+  ["deref reduced"     "9"      "(deref (reduced 9))"]
   ["unreduced wrapped" "9"      "(unreduced (reduced 9))"]
   ["unreduced plain"   "9"      "(unreduced 9)"]
   ["not-empty full"    "[1]"    "(not-empty [1])"]