Increase sensitivity of Supply.batch(:seconds) x 1000

Instead of using "per second" granularity for batching based on elapsed
time, allow for millisecond granularity.  The value still needs to be
specified in seconds.  So, to get batching per millisecond, one would
have to specify "seconds => 0.001"

src/core.c/Supply-coercers.pm6

@@ -382,21 +382,23 @@
         supply {
             my int $max = $elems >= 0 ?? $elems !! 0;
             my $batched := nqp::list;
-            my $last_time;
             sub flush(--> Nil) {
                 emit($batched);
                 $batched := nqp::list;
             }
             sub final-flush(--> Nil) {
-                flush if nqp::elems($batched);
+                emit($batched) if nqp::elems($batched);
             }
 
             if $seconds {
-                $last_time = time div $seconds;
+                my int $msecs = ($seconds * 1000).Int;
+                my int $last_time =
+                  nqp::div_i(nqp::mul_n(nqp::time_n,1000e0),$msecs);
 
                 if $elems > 0 { # and $seconds
                     whenever self -> \val {
-                        my $this_time = time div $seconds;
+                        my int $this_time =
+                          nqp::div_i(nqp::mul_n(nqp::time_n,1000e0),$msecs);
                         if $this_time != $last_time {
                             flush if nqp::elems($batched);
                             $last_time = $this_time;
@@ -411,7 +413,8 @@
                 }
                 else {
                     whenever self -> \val {
-                        my $this_time = time div $seconds;
+                        my int $this_time =
+                          nqp::div_i(nqp::mul_n(nqp::time_n,1000e0),$msecs);
                         if $this_time != $last_time {
                             flush if nqp::elems($batched);
                             $last_time = $this_time;