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/numbers-spec.janet

@@ -131,5 +131,6 @@
   ["rand-int in range"  "true" "(let [r (rand-int 5)] (and (integer? r) (>= r 0) (< r 5)))"]
   ["rand-int zero"      "0"    "(rand-int 1)"]
   ["rand in [0,1)"      "true" "(let [r (rand)] (and (>= r 0) (< r 1)))"]
+  ["rand n in [0,n)"    "true" "(let [r (rand 10)] (and (>= r 0) (< r 10)))"]
   ["rand-nth member"    "true" "(contains? #{:a :b :c} (rand-nth [:a :b :c]))"]
   ["rand-nth single"    ":x"   "(rand-nth [:x])"])