test: comprehensive spec — regex + sorted colls + random/predicate gaps

Filling the biggest untested clojure.core areas found in a coverage audit
(168 of 506 provided fns had no spec). New + expanded suites:

- regex-spec.janet (20): #"…" literals, regex?, re-find/re-matches/re-seq
  (match/no-match/groups), re-pattern, and clojure.string split/replace with
  regex (incl $1 backrefs). Whole area was previously unspecced.
- sorted-spec.janet (14): sorted-map/sorted-set construction + ordering, sorted?,
  subseq/rsubseq. Pins the working subset — get/conj/assoc/keys/vals on sorted
  colls and the by-comparator ctors are not yet first-class (jolt-ti9).
- predicates-spec +14: seqable?, integer?, reduced?/unreduced, not-empty.
- numbers-spec +5: rand/rand-int/rand-nth invariants.

Fix: sorted? was bound to core-sorted-map? so it returned false for sorted-sets;
now true for both sorted maps and sets (core-sorted?).

Filed: jolt-ti9 (sorted collections incomplete: get/conj/assoc/keys/vals don't
operate on the sorted wrapper; sorted-*-by ignore the comparator).

Gate green incl full jpm build + jpm test.

test/spec/sorted-spec.janet

@@ -0,0 +1,29 @@
+# Specification: sorted collections (sorted-map / sorted-set, subseq/rsubseq).
+#
+# NOTE: sorted collections are only partially first-class in Jolt — get/conj/assoc/
+# contains?/keys/vals on a sorted coll, and the by-comparator constructors, are NOT
+# yet wired up (jolt-ti9). This spec pins the behavior that DOES work (construction,
+# SEQ ordering, subseq/rsubseq, sorted?, first) so it can't regress; the broken ops
+# are tracked in jolt-ti9. (vec coerces the seq to a vector so expecteds are vector
+# literals rather than quoted lists.)
+(use ../support/harness)
+
+(defspec "sorted / construction & ordering"
+  ["sorted-set orders"   "[1 2 3]" "(vec (seq (sorted-set 3 1 2)))"]
+  ["sorted-set dedupes"  "[1 2 3]" "(vec (seq (sorted-set 3 1 2 1 3)))"]
+  ["sorted-set numeric"  "[1 2 10]" "(vec (seq (sorted-set 10 1 2)))"]
+  ["sorted-map ordered entries" "[[:a 1] [:b 2] [:c 3]]" "(vec (seq (sorted-map :c 3 :a 1 :b 2)))"]
+  ["first is min"        "1"       "(first (sorted-set 5 3 9 1))"])
+
+(defspec "sorted / sorted?"
+  ["sorted-set"      "true"   "(sorted? (sorted-set 1))"]
+  ["sorted-map"      "true"   "(sorted? (sorted-map :a 1))"]
+  ["plain set"       "false"  "(sorted? #{1})"]
+  ["plain map"       "false"  "(sorted? {:a 1})"]
+  ["vector"          "false"  "(sorted? [1 2])"])
+
+(defspec "sorted / subseq & rsubseq"
+  ["subseq >="       "[3 4 5]" "(vec (subseq (sorted-set 1 2 3 4 5) >= 3))"]
+  ["subseq <"        "[1 2]"   "(vec (subseq (sorted-set 1 2 3 4 5) < 3))"]
+  ["subseq range"    "[2 3 4]" "(vec (subseq (sorted-set 1 2 3 4 5) > 1 < 5))"]
+  ["rsubseq <="      "[3 2 1]" "(vec (rsubseq (sorted-set 1 2 3 4 5) <= 3))"])