Chez Phase 2 (inc I+J): first-class vars + scalar natives

inc I (jolt-n7rz) — vars as first-class objects. (var x)/#'x lowered a
:the-var IR op the Chez emitter didn't handle (57 emit-fails, the biggest
bucket); emit it to the rt.ss var-cell and shim the static var ops in
vars.ss: var?/var-get/deref/var-as-IFn/var =/pr-str (#'ns/name) + a native
bound? (the overlay reads (get v :root), nil on a var-cell record). def now
RETURNS the var (#'ns/name) like Clojure — def-var!/declare-var! yield the
cell, not the value — so (var? (def x 1)) is true and pr-str-of-var/defn
pass (un-allowlisted). Dynamic binding (binding/with-bindings*/var-set/
thread-bound?) stays a follow-up; those crash on nil host prims (safe).
Var def-time metadata (^:private/^Type/doc) isn't captured yet — allowlisted.

inc J (jolt-snry) — scalar natives. natives-misc.ss: a juuid record
(random-uuid v4 / parse-uuid / uuid? / #uuid pr-str / str), a %-format
engine (%d/%s/%.Nf/%x/%c/%%; printf rides on it), a jtagged record
(tagged-literal + :tag/:form + #tag pr-str), bigint/biginteger as
near-identity over the all-flonum model. Overlay names (uuid?/random-uuid/
parse-uuid/tagged-literal?) re-asserted in post-prelude.ss.

Prelude parity 1898 -> 1951, 0 new divergences. Floor raised to 1951.

host/chez/emit.janet

@@ -429,6 +429,9 @@
                (string "(var-deref " (chez-str-lit (get node :ns)) " "
                        (chez-str-lit (get node :name)) ")")))
     :host  (errorf "emit: unsupported host ref `%s` (no host interop on Chez yet)" (get node :name))
+    # (var x) / #'x -> the var cell itself (the rt.ss var-cell, a first-class var
+    # object). var?/var-get/deref/invoke/= operate on it (vars.ss).
+    :the-var (string "(jolt-var " (chez-str-lit (get node :ns)) " " (chez-str-lit (get node :name)) ")")
     :if    (let [test (get node :test)
                  t (if (returns-scheme-bool? test) (emit test)
                        (string "(jolt-truthy? " (emit test) ")"))]