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.

docs/rfc/0003-transients.md

@@ -22,6 +22,11 @@ A transient is a tagged Janet table wrapping a *native* mutable host value
   key for the rebuilt persistent map.
 - transient set — `:kind :set :tbl TABLE` mapping `canon-key(x)` → `x`.
 
+`transient` accepts pvecs, mutable-build arrays, tuples (reader vectors and
+map entries — added in the seed-shrink rounds so `(into [] (first {:a 1}))`
+works through the vector fast path), sets, phms, and untagged struct maps.
+Sorted collections are rejected, as on the JVM (not editable).
+
 The bang ops (`conj!`, `assoc!`, `dissoc!`, `disj!`, `pop!`) mutate that host
 value in place and return the transient — O(1) per op (amortized for array
 push). `persistent!` rebuilds a persistent value from the host value and