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/java/io.ss

@@ -412,6 +412,11 @@
     ;; method (a no-op for in-memory streams); absent method -> no-op.
     ((htable? x) (guard (e (#t jolt-nil)) (record-method-dispatch x "close" jolt-nil)) jolt-nil)
     ((jfile? x) jolt-nil)
+    ;; a deftype/defrecord that implements a `close` method (java.io.Closeable /
+    ;; AutoCloseable, e.g. tools.reader's reader types) closes through it — the
+    ;; same method (.close x) would dispatch to.
+    ((and (jrec? x) (jrec-cl x "close"))
+     (record-method-dispatch x "close" jolt-nil) jolt-nil)
     (else
      (let ((closef (jolt-get x (keyword #f "close") jolt-nil)))
        (if (and (not (jolt-nil? closef)) (procedure? closef))