Clojure 1.13 parity: req!, checked-keys destructuring, keyword array maps

Bring the language up to the 1.13.0-alpha1 changes that apply off the JVM:

- req! (CLJ-2949): a get-variant that throws "Expected key: k" on a missing
  key, without nil-punning. The primitive behind checked destructuring.
- Checked-keys destructuring (CLJ-2961): :keys!/:syms!/:strs! bind and throw
  when a key is absent; keys after & are declared-only (required for the !
  variants, accepted otherwise) and create no binding.
- & is no longer a legal local binding in let/loop (CLJ-2954).
- Keyword-only array maps grow to 64 entries before going hash (was 8),
  across the literal, assoc, and transient paths, so the common keyword map
  keeps insertion order up to 64.

Skipped CLJ-2891 (JVM __init bytecode, JVM-only). 1.13 is still alpha, so
this tracks alpha1 and may shift. Regression tests in test/chez/unit.edn
(ahead of the JVM 1.12.5 the corpus certifies against). Seed re-minted.

jolt-core/clojure/core/22-coll.clj

@@ -89,6 +89,21 @@
              (recur nxt (next ks))))
          m)))))
 
+(defn req!
+  "Returns the value mapped to key k in map m, like `get`, but throws
+  IllegalArgumentException when k is not present. Unlike `get`, does not nil-pun:
+  a key present with a nil value returns nil, an absent key throws. The primitive
+  behind checked-keys destructuring (:keys! / :syms! / :strs!)."
+  {:added "1.13"}
+  [m k]
+  ;; a fresh map is its own identity, so a present-but-nil value is distinguished
+  ;; from an absent key (same trick as get-in's sentinel).
+  (let [sentinel (hash-map)
+        v (get m k sentinel)]
+    (if (identical? sentinel v)
+      (throw (new IllegalArgumentException (str "Expected key: " k)))
+      v)))
+
 ;; find-based, so nil RESULTS are cached too; args canonicalize as a collection key.
 (defn memoize [f]
   (let [mem (atom (hash-map))]