Unchecked / *unchecked-math* arithmetic wraps to signed 64-bit

clojure.core's unchecked-* (and +/-/*/inc/dec under *unchecked-math*) are long
ops that WRAP on overflow; jolt's checked arithmetic is arbitrary-precision and
its unchecked-* were plain non-wrapping (+ x y), diverging from the JVM. Now they
truncate to the low 64 bits as a signed long, matching Clojure:

  (unchecked-add 9223372036854775807 1)        => -9223372036854775808
  (unchecked-multiply 9223372036854775807 …)   => 1

- host/chez/seq.ss: jolt-wrap64 + binary jolt-unc{add,sub,mul,inc,dec,neg}2 and
  the variadic clojure.core/unchecked-* fns (def-var!'d in natives-seq.ss, where
  def-var! is bound). The overlay's plain unchecked-* defns are removed.
- backend lng-ops: unchecked-+/-/* emit the wrapping jolt-unc* helpers (the
  raising fx ops can't wrap on Chez's 61-bit fixnums); unchecked-inc/dec too.
- *unchecked-math* is honored: the analyzer reads it (jolt.host/unchecked-math?)
  and rewrites +/-/*/inc/dec to their unchecked-* for the rest of a file that
  (set!)s it, like the JVM.
- jolt->fx: a ^long value that overflows the 61-bit fixnum range passes through
  as an exact integer instead of erroring (a full-width long from wrapping math).

Also adds Long/bitCount / numberOfLeadingZeros / reverse and Math/getExponent /
scalb (test.check's splittable PRNG uses them).

This lets clojure.test.check load and run quick-check on jolt. re-mint (analyzer/
backend/overlay are seed sources). make test green (+6 corpus rows, 0 new
divergences, numeric gate updated), shakesmoke byte-identical.

host/chez/natives-seq.ss

@@ -228,3 +228,14 @@
       (list->cseq (reverse (seq->list (jolt-seq coll))))
       (jolt-throw (jolt-ex-info "rseq requires a vector or sorted collection" (jolt-hash-map)))))
 (def-var! "clojure.core" "rseq" jolt-rseq)
+
+;; clojure.core/unchecked-* — host-defined wrapping (Java long) arithmetic from
+;; seq.ss. def-var!'d here because def-var! isn't bound when seq.ss loads.
+(let ((d! (lambda (n v) (def-var! "clojure.core" n v))))
+  (d! "unchecked-add" jolt-unchecked-add)        (d! "unchecked-add-int" jolt-unchecked-add)
+  (d! "unchecked-subtract" jolt-unchecked-sub)   (d! "unchecked-subtract-int" jolt-unchecked-sub)
+  (d! "unchecked-multiply" jolt-unchecked-mul)   (d! "unchecked-multiply-int" jolt-unchecked-mul)
+  (d! "unchecked-negate" jolt-uncneg)            (d! "unchecked-negate-int" jolt-uncneg)
+  (d! "unchecked-inc" jolt-uncinc)               (d! "unchecked-inc-int" jolt-uncinc)
+  (d! "unchecked-dec" jolt-uncdec)               (d! "unchecked-dec-int" jolt-uncdec)
+  (d! "unchecked-divide-int" jolt-unchecked-div) (d! "unchecked-remainder-int" jolt-unchecked-rem))