Move the compaction warning below the table

Having it between the table header and the data makes the data table
harder to read so we should put it somewhere less obtrusive

Author: eightbitraptor

harness-ractor/harness.rb

@@ -130,6 +130,7 @@ def run_benchmark_gc(warmup_itrs, bench_itrs, block, ractor_args, gc_config:)
     end
     gc_by_ractors[rs] = group
   end
+  print_gc_legend
 
   return_results(warmups.values.flatten, stats.values.flatten, warmup_by_ractors: warmups, bench_by_ractors: stats, **ractor_gc_results(gc_by_ractors, gc_config))
 end
@@ -138,6 +139,9 @@ def print_gc_header(prefix)
   header = prefix + "   gc_total   marking  sweeping  gc_count     major     minor    global"
   CONTROLLER_GC_SERIES.each_value { |(_stat_key, label)| header << " %9s" % label }
   puts header
+end
+
+def print_gc_legend
   puts "(* controller-observed compacting cycles; may overlap global counts and is not additive.)" if CONTROLLER_GC_SERIES.any?
 end
 
@@ -277,6 +281,8 @@ def run_scenario_benchmark(bench_itrs, gc_config:, &scenario)
     gc_by_ractors[count] = group.merge(series)
   end
 
+  print_gc_legend if RACTOR_GC_ENABLED
+
   medians = counts.to_h { |count| [count, memory_summary(memory[count])] }
   print_memory_metrics(medians)
 

test/ractor_gc_harness_test.rb

@@ -222,8 +222,12 @@ def run_workload(body, env: {})
       assert_equal %w[0 1 2], data['gc_by_ractors'].keys.sort
 
       if data['gc_by_ractors'].values.any? { |group| group.key?('gc_controller_compact_count_bench') }
-        assert_includes stdout, '(* controller-observed compacting cycles; may overlap global counts and is not additive.)',
-          'a starred stdout column must always come with the exact legend line'
+        legend = '(* controller-observed compacting cycles; may overlap global counts and is not additive.)'
+        lines = stdout.lines(chomp: true)
+        legend_index = lines.index(legend)
+        refute_nil legend_index, 'a starred stdout column must always come with the exact legend line'
+        last_row_index = lines.rindex { |line| line.match?(/\A2\s+#2:/) }
+        assert_operator legend_index, :>, last_row_index, 'the legend must follow the last table row'
       end
 
       expected_worker_keys = %w[