delay exception memoization, deftype cross-protocol method merge, more map-like dispatch

Further clojure.core.cache fixes (198 -> 257 of its assertions):

- delay: a throwing body re-ran on every force and never became realized?. Run it
  once like Clojure's Delay — cache the exception, mark realized, re-throw the same
  on each deref. Fixes value-fn memoization / cache-stampede protection.
- deftype/defrecord: a method name appearing in two protocols with different
  arities (data.priority-map's seq is in IPersistentMap [this] AND Sorted
  [this asc]) registered per-protocol and shadowed; merge clauses by name across
  all protocols into one multi-arity fn.
- empty?/peek/pop (IPersistentStack) dispatch through a deftype's methods; (= a-
  deftype other) uses its equiv method (so caches compare to their backing map);
  seq handles a host iterator (iterator-seq over .iterator).
- pop of an empty PersistentQueue returns it, like the JVM (was an error).

JVM-certified corpus rows. make test + shakesmoke green.

host/chez/concurrency.ss

@@ -228,15 +228,21 @@
 ;; (delay body) -> (make-delay (fn [] body)) (overlay macro); force/deref run the
 ;; thunk once under a lock and cache the value (JVM delays are thread-safe). force
 ;; (overlay) is (if (delay? x) (deref x) x), so it works once delay?/deref do.
-(define-record-type jolt-delay (fields thunk (mutable realized?) (mutable value) mu)
+(define-record-type jolt-delay (fields thunk (mutable realized?) (mutable value) (mutable exn) mu)
   (nongenerative jolt-delay-v1))
-(define (jolt-make-delay thunk) (make-jolt-delay thunk #f jolt-nil (make-mutex)))
+(define (jolt-make-delay thunk) (make-jolt-delay thunk #f jolt-nil #f (make-mutex)))
+;; run the thunk once, like Clojure's Delay: if it throws, cache the exception
+;; (the delay IS realized) and re-throw it on every deref — do NOT re-run the
+;; body (so value-fns memoize and there is no cache-stampede / retried side
+;; effect). Store the exception inside the lock, re-raise outside it so the mutex
+;; is always released.
 (define (jolt-delay-force d)
   (with-mutex (jolt-delay-mu d)
     (unless (jolt-delay-realized? d)
-      (jolt-delay-value-set! d (jolt-invoke (jolt-delay-thunk d)))
-      (jolt-delay-realized?-set! d #t)))
-  (jolt-delay-value d))
+      (guard (e (#t (jolt-delay-exn-set! d e) (jolt-delay-realized?-set! d #t)))
+        (jolt-delay-value-set! d (jolt-invoke (jolt-delay-thunk d)))
+        (jolt-delay-realized?-set! d #t))))
+  (if (jolt-delay-exn d) (raise (jolt-delay-exn d)) (jolt-delay-value d)))
 
 ;; --- deref extension --------------------------------------------------------
 ;; Chain the fully-built jolt-deref (atoms/vars/volatiles/reduced) with futures,