core: enforce fn arity in both modes (jolt-6xn); canonical seq-to-map-for-destructuring

Fixed arities now throw Clojure's ArityException shape — 'Wrong number of
args (N) passed to: name' — on any count mismatch; variadic arities on fewer
than their fixed params. The compiled path already enforced fixed arities via
janet's native fn check and multi-arity dispatch; this adds the check to the
interpreter's single-arity closures (the oracle was silently dropping extra
args and giving a raw tuple-index error for missing ones) and guards the
compiled single-variadic wrapper's minimum. Messages carry the fn name when
there is one. 16 spec rows; the update.cljc suite row flipped green (4703 ->
4704).

Enforcement exposed that seq-to-map-for-destructuring had drifted: the spec
row called the 1-arity fn with two args, and the body silently dropped a
trailing unpaired element. Replaced with the canonical Clojure 1.11 version
(even pairs build the map, a single trailing element passes through — so
(f {:b 2}) kwargs calls work — and an unpaired key throws).

Also: transients RFC notes tuple support from the seed-shrink rounds.

test/spec/untested-vars-spec.janet

@@ -157,7 +157,10 @@
   ["special-symbol? if" "true" "(special-symbol? (quote if))"]
   ["special-symbol? fn name" "false" "(special-symbol? (quote foo))"]
   ["destructure expands" "true" "(pos? (count (destructure (quote [[a b] x]))))"]
-  ["seq-to-map-for-destructuring" "{:a 1}" "(seq-to-map-for-destructuring (quote (:a 1)) nil)"]
+  ["seq-to-map-for-destructuring" "{:a 1}" "(seq-to-map-for-destructuring (quote (:a 1)))"]
+  ["s2m trailing map passes through" "{:b 2}" "(seq-to-map-for-destructuring (list {:b 2}))"]
+  ["s2m unpaired key throws" :throws "(seq-to-map-for-destructuring (quote (:a 1 :b)))"]
+  ["s2m kwargs trailing map call" "2" "((fn [& {:keys [b]}] b) {:b 2})"]
   ["*clojure-version* major" "1" "(:major *clojure-version*)"]
   ["*ns* user" "\"user\"" "(str *ns*)"]
   ["*1 nil outside repl" "nil" "*1"]