Chez Phase 2 (inc U): list? + map-entry-as-vector + clojure.walk (jolt-75sv)

list? was nil on Chez because one cseq record backs both lists and lazy/
realized seqs. Add a list? marker field (cseq v2) set only on the HEAD cell
of a list -- (list ...), quoted list literals, cons, reverse, conj onto a
list. rest/next/seq/map therefore yield unmarked seq cells, so they are
seqs and not list?, matching the seed (where rest-of-a-list is a non-list
seq). Empty () is treated as a list.

vector?: drop the map-entry exclusion. Clojure's MapEntry implements
IPersistentVector and the seed agrees -- (vector? (first {:a 1})) is true.
Only dot-forms' coll dispatch read jolt-vector?, where a 2-vector entry is
correct.

clojure.walk + clojure.template join the prelude stdlib tier. The driver
now evals each stdlib ns's requires -- and the ns form's (:require ...)
clause -- so an aliased ref (template's walk/postwalk-replace) resolves at
emit time instead of lowering to an Unknown class host-static. ns forms are
evaled for that side effect but not emitted, so the runtime *ns* doesn't
leak to the last stdlib ns.

Parity 2163 -> 2176, 0 new divergences. New test/chez/_walk.janet 39/39.

host/chez/collections.ss

@@ -203,9 +203,11 @@
 (define (jolt-conj1 coll x)
   (cond ((pvec? coll) (pvec-conj coll x))   ; nil is a valid vector/set element
         ((pset? coll) (pset-conj coll x))
-        ;; a list/seq conjs by PREPENDING (seq.ss: cseq / empty-list)
-        ((cseq? coll) (cseq-realized x coll))
-        ((empty-list-t? coll) (cseq-realized x jolt-nil))
+        ;; a list/seq conjs by PREPENDING (seq.ss: cseq / empty-list). conj onto a
+        ;; list stays a list, conj onto a lazy/realized seq yields a seq cell (a
+        ;; Cons) — list?-preserving, matching the seed.
+        ((cseq? coll) (if (cseq-list? coll) (cseq-list x coll) (cseq-realized x coll)))
+        ((empty-list-t? coll) (cseq-list x jolt-nil))
         ((pmap? coll)
          (cond ((jolt-nil? x) coll)                                   ; (conj m nil) = m
                ((pmap? x) (pmap-fold x (lambda (k v m) (pmap-assoc m k v)) coll))   ; merge