Make native array.sum faster

- 1.2x as fast by default by not using Any::sum anymore
- 35x as fast with specifying the :wrap named variable

The latter will do *all* calculations in native ints: should the sum of
the native array exceed the size of the "int" type, then it will silently
wrap.  This may or may not be what you want, hence the optional named variable.

src/core/native_array.pm6

@@ -988,6 +988,34 @@ my class array does Iterable {
 #- PLEASE DON'T CHANGE ANYTHING ABOVE THIS LINE
 #- end of generated part of intarray role -------------------------------------
 
+        method sum(intarray:D: :$wrap) {
+            nqp::if(
+              (my int $elems = nqp::elems(self)),
+              nqp::stmts(
+                (my int $i),
+                nqp::if(
+                  $wrap,
+                  nqp::stmts(
+                    (my int $sum = nqp::atpos_i(self,0)),
+                    nqp::while(
+                      nqp::islt_i(($i = nqp::add_i($i,1)),$elems),
+                      $sum = nqp::add_i($sum,nqp::atpos_i(self,$i))
+                    ),
+                    $sum
+                  ),
+                  nqp::stmts(
+                    (my Int $Sum = nqp::atpos_i(self,0)),
+                    nqp::while(
+                      nqp::islt_i(($i = nqp::add_i($i,1)),$elems),
+                      $Sum = $Sum + nqp::atpos_i(self,$i)
+                    ),
+                    $Sum
+                  )
+                )
+              ),
+              0
+            )
+        }
         method join(intarray:D: $delim = '') {
             my int $elems = nqp::elems(self);
             my $list     := nqp::setelems(nqp::list_s,$elems);