Fix six JVM divergences surfaced by rewrite-clj

Running the rewrite-clj test suite under jolt exposed six bugs, each fixed here:

- `for`/`doseq` `:let` bindings never went through `destructure`, so a
  destructuring pattern (`:let [{:keys [y]} x]`) hit `let*` raw and failed to
  compile. Emit `let`, like Clojure.
- `with-open` couldn't close a deftype/defrecord that implements a `close` method
  (java.io.Closeable / AutoCloseable, e.g. tools.reader's readers) — `__close`
  only knew jhost readers and map `:close` fns. Dispatch a record's `close`.
- A deftype/defrecord method param named like a field didn't shadow the field
  (the field's let-binding wrapped the params). Params now shadow, as in Clojure.
- A deftype whose simple name collided with a built-in host class clobbered it in
  the global ctor table, so `(java.io.PushbackReader. …)` built tools.reader's
  same-named deftype. Register deftypes/built-ins by FQN, don't let a deftype
  overwrite a built-in's simple name, and qualify a bare `(Name. …)` to the
  deftype's FQN only in the ns that defined it.
- `clojure.walk` was lazy over a non-list seq (missing `doall`), so a walk whose
  fn has side effects read stale state. Make it eager, like Clojure.
- `Character/isWhitespace` used an ASCII-only check that missed U+2028 and other
  Unicode whitespace. Use the JVM's Unicode set (minus the no-break spaces it
  excludes).

Regressions: corpus rows (for-let destructure, method-param shadow, walk eager,
isWhitespace), a unit row (with-open closes a record), and smoke checks (the
class-name collision, run in a fresh -e process so the deftype doesn't leak).

One divergence remains unfixed: a submatch from a losing regex alternation branch
leaks when the winning branch has a quantified group (a bug in the vendored
irregex engine, not jolt) — tracked separately.

host/chez/host-contract.ss

@@ -430,6 +430,19 @@
 (define (hc-record-ctor-key ctx name)
   (let ((nm (hc-record-tag-name name)))
     (or (and nm (chez-find-ctor-key nm (chez-current-ns))) jolt-nil)))
+;; The fully-qualified deftype tag ("ns.Name") IFF `class` names a deftype DEFINED
+;; in the ctx's compile ns — the analyzer qualifies a bare (Name. …) to it, so a
+;; deftype doesn't shadow a same-named built-in host class in an unrelated ns
+;; (rewrite-clj imports java.io.PushbackReader; tools.reader defines its own). Strict:
+;; only this ns's own def (the preferred shape key) counts, not the global
+;; simple-name fallback, so a ns that merely uses the built-in resolves nil.
+(define (hc-deftype-ctor-class ctx class)
+  (let* ((nm (jolt-str-render-one class))
+         (cns (hc-current-ns ctx))
+         (key (string-append cns "/->" nm)))
+    (if (hashtable-ref chez-record-shapes-tbl key #f)
+        (string-append cns "." nm)
+        jolt-nil)))
 ;; record + protocol-method shapes for the inference, from the runtime registries
 ;; (records.ss) populated as deftype/defprotocol forms load.
 (define (hc-record-shapes ctx) (chez-record-shapes-map))
@@ -505,6 +518,7 @@
   (def-var! "jolt.host" "form-syntax-quote-lower" hc-syntax-quote-lower)
   (def-var! "jolt.host" "record-type?" hc-record-type?)
   (def-var! "jolt.host" "record-ctor-key" hc-record-ctor-key)
+  (def-var! "jolt.host" "deftype-ctor-class" hc-deftype-ctor-class)
   (def-var! "jolt.host" "record-shapes" hc-record-shapes)
   (def-var! "jolt.host" "protocol-methods" hc-protocol-methods)
   (def-var! "jolt.host" "inline-enabled?" hc-inline-enabled?)