Chez numeric tower: exact ints / Ratio / double for JVM parity (jolt-n6al)

jolt was all-flonum (one :number type, inherited from Janet whose only number
type is a double). The Chez runtime has a full numeric tower, so the zero-Janet
path now carries it = JVM Clojure semantics:

  (/ 1 2)      => 1/2      (exact Ratio, was 0.5)
  (integer? 3) => true   (integer? 3.0) => false   (float? 3.0) => true
  (ratio? (/ 1 2)) => true   (= 3 3.0) => false   (== 3 3.0) => true
  (+ 1 2) => 3 (exact)   (/ 1.0 2) => 0.5 (double)

jolt= was already exactness-aware (values.ss) and == is value-equality, so
=/== match the JVM split. The reader preserves exactness (integer literals exact,
a/b ratios exact rationals, decimals/exponents flonums); backend_scheme emit-const
renders exact ints/ratios and flonums faithfully; the value-position arithmetic,
count, int, compare, bit ops, parseLong, string .length/.indexOf, range,
timestamps, and array bytes return exact integers (= JVM int/long) instead of
coercing to flonum. double/parseDouble/clojure.math floor|ceil|signum stay double.

Only the zero-Janet path carries the tower (the Janet reader loses exactness into
a double before emit). The prelude/all-flonum path is unaffected for compiled code;
the runtime reader is shared, so a couple of all-flonum reader assertions become
value (==) assertions. ~16 numeric corpus cases now give the JVM tower value vs the
Janet-era :expected and are allowlisted as tower divergences (Chez == reference
JVM) pending the corpus flip to JVM (jolt-ecz0). No BigDecimal type (1M).

Re-minted. zero-janet 2682 (floor 2698->2682, the reclassified tower cases), 0 new
divergences; fixpoint 10/10, bootstrap 6/6, spine 35/35, cli 49/49; Janet gate 155
files 0 failed.

host/chez/inst-time.ss

@@ -88,7 +88,7 @@
           (else (fail)))))
     (unless (= i len) (fail))
     (let ((base-s (+ (* (days-from-civil year month day) 86400) (* hh 3600) (* mm 60) ss)))
-      (make-jinst (exact->inexact (- (+ (* base-s 1000) frac-ms) (* off-s 1000)))))))
+      (make-jinst (- (+ (* base-s 1000) frac-ms) (* off-s 1000))))))
 
 ;; --- canonical print form: yyyy-MM-ddThh:mm:ss.fff-00:00 (UTC) ---------------
 (define (pad2 n) (if (< n 10) (string-append "0" (number->string n)) (number->string n)))
@@ -223,7 +223,9 @@
 (define (mk-local ms) (make-jhost "local-dt" (vector ms)))
 (define (mk-formatter pat) (make-jhost "dt-formatter" (vector pat)))
 (define (fmt-pat f) (vector-ref (jhost-state f) 0))
-(define (now-ms) (exact->inexact (now-millis)))   ; now-millis from host-static.ss
+(define (now-ms) (now-millis))   ; exact ms (= JVM long); now-millis from host-static.ss
+;; coerce a user-supplied ms (exact or flonum) to an exact integer for storage.
+(define (ms->exact ms) (exact (round ms)))
 
 (register-host-methods! "instant"
   (list (cons "atZone" (lambda (self zone) (mk-zoned (ms-of self))))
@@ -262,7 +264,7 @@
         (cons "ofLocalizedTime" (lambda (fs) (style-fmt 'time fs)))
         (cons "ofLocalizedDateTime" (lambda (fs) (style-fmt 'datetime fs)))))
 (register-class-statics! "Instant"
-  (list (cons "ofEpochMilli" (lambda (ms) (mk-instant (exact->inexact ms))))
+  (list (cons "ofEpochMilli" (lambda (ms) (mk-instant (ms->exact ms))))
         (cons "now" (lambda () (mk-instant (now-ms))))))
 (register-class-statics! "ZoneId"
   (list (cons "systemDefault" (lambda () (make-jhost "zone-id" (vector "system"))))
@@ -283,7 +285,7 @@
 ;; or (Date. another-date) -> a jinst (ms-of accepts a number / jinst / instant), so
 ;; .getTime / inst? / instance? Date|Timestamp work. (jolt-dcmm)
 (define (date-ctor . args)
-  (make-jinst (if (null? args) (now-ms) (exact->inexact (ms-of (car args))))))
+  (make-jinst (if (null? args) (now-ms) (ms->exact (ms-of (car args))))))
 (register-class-ctor! "Date" date-ctor)
 (register-class-ctor! "java.util.Date" date-ctor)
 (register-class-ctor! "Timestamp" date-ctor)