rand_curveball: no need to consider groups with maximum richness

These can be added to the final result directly.

lib/Biodiverse/Randomise/CurveBall.pm

@@ -120,6 +120,12 @@ END_PROGRESS_TEXT
     printf "[RANDOMISE] Randomise using curveball algorithm for %s labels from %s groups\n",
         scalar @sorted_labels, scalar @sorted_groups;
 
+    #  No need to consider groups that cannot be swapped out.
+    #  Could use a binary search but this is only done once per iteration.
+    if (keys %has_max_richness) {
+        @sorted_groups = grep {!exists $has_max_richness{$_}} @sorted_groups;
+    }
+
     $progress_bar->reset;
 
     #  Basic algorithm:

t/28-Randomisation.t

@@ -143,6 +143,15 @@ sub test_rand_structured_richness_same {
         my $gp = "$x:$y";
         $bd->add_element (group => $gp, allow_empty_groups => 1);
     }
+    #  add a cell with all possible labels
+    {
+        my $x = -100 * $c + $c / 2;
+        my $y = -$c / 2;
+        my $gp = "$x:$y";
+        foreach my $label ($bd->get_labels) {
+            $bd->add_element(group => $gp, label => $label);
+        }
+    }
 
     #  name is short for test_rand_calc_per_node_uses_orig_bd
     my $sp = $bd->add_spatial_output (name => 'sp');