Host shims and protocol fixes shaken out by aws-api

Running cognitect aws-api's pure test namespaces (signing/shapes/protocols/
util/retry/endpoints) surfaced general gaps:

- extend-protocol/extend-type accept a computed class type, e.g.
  (Class/forName "[B") for the byte-array class — the byte-array idiom data.json
  and aws-api use. The macro grouping handled only symbol/nil heads (it crashed on
  a list type); type->name resolves a Class value via .getName; a byte-array
  dispatches on the "[B" host tag.
- java.nio.ByteBuffer over a jolt byte-array (wrap/allocate/get/put/array/
  remaining/position/limit/duplicate/flip), plus extend-protocol to it.
- java.util.Arrays (equals/copyOf/copyOfRange/fill) and java.util.Random
  (nextBytes/nextInt/…).
- java.net.URI/create and clojure.lang.RT/baseLoader statics.
- clojure.core.async/promise-chan (deliver-once, peek-don't-pop).
- a failed java.time parse throws DateTimeParseException (typed), so
  (catch DateTimeParseException …) matches it instead of leaking an untyped
  condition.

The XML side lives in the jolt-lang/xml library (libxml2 over jolt.ffi); ByteBuffer
stays in core as a generic java.nio primitive.

Gate: make test green (corpus +6 JVM-certified rows, 0 NEW divergence; unit
553/553; SCI 211).

host/chez/inst-time.ss

@@ -180,7 +180,11 @@
 (define (parse-ms pattern input)
   (let ((pn (string-length pattern)) (inn (string-length input))
         (y 1970) (mo 1) (d 1) (hh 0) (mi 0) (ss 0) (pm 'none))
-    (define (pfail) (error #f (string-append "ParseException: unparseable date \"" input "\"")))
+    ;; a parse failure is a java.time.format.DateTimeParseException (typed, so a
+    ;; (catch DateTimeParseException …) over a bad date matches), like the JVM.
+    (define (pfail)
+      (jolt-throw (jolt-host-throwable "java.time.format.DateTimeParseException"
+                                       (string-append "unparseable date \"" input "\"") jolt-nil)))
     (define (run-len i c) (let loop ((j i)) (if (and (< j pn) (char=? (string-ref pattern j) c)) (loop (+ j 1)) (- j i))))
     ;; read up to `maxw` digits (#f = unbounded). A fixed-width field (k>=2, e.g.
     ;; HHmm) caps the read at its run length so adjacent numeric fields split.