Implement the ability to use multiple harnesses

This commit introduces a harness that can be used to chain two (or more)
harnesses together.

For example. To run a Ractor test with Vernier you can wrap the ractor
harness with the vernier one as follows

HARNESS_CHAIN="vernier,ractor" ruby -Iharness-chain benchmarks-ractor/optcarrot/benchmark.rb

Author: luke-gruber

harness-chain/harness.rb

@@ -0,0 +1,52 @@
+require_relative '../harness/harness-common'
+
+# Ex: HARNESS_CHAIN="vernier,ractor"
+# Wraps the ractor harness in ther vernier harness
+CHAIN = ENV['HARNESS_CHAIN'].to_s.split(',')
+CHAIN.reject! { |el| el.to_s.strip.empty? }
+if CHAIN.size < 2
+  $stderr.puts "You need to chain at least 2 harnesses. Exiting."
+  exit 1
+end
+
+if CHAIN.include?("vernier") && CHAIN.last != "vernier"
+  require_relative "../harness/harness-extra"
+  def run_enough_to_profile(n, **kwargs, &block)
+    block.call
+  end
+end
+
+$current_harness = nil
+$benchmark_methods = []
+
+class Object
+  def self.method_added(name)
+    if name ==  :run_benchmark && $current_harness
+      $benchmark_methods << [$current_harness, Object.instance_method(name)]
+    end
+  end
+end
+
+def run_benchmark(n, **kwargs, &block)
+  CHAIN.each do |h|
+    begin
+      path = "../harness-#{h}/harness"
+      $current_harness = h
+      require_relative path
+    rescue LoadError => e
+      if e.path == path
+        $stderr.puts "Can't find harness harness-#{h}/harness.rb. Exiting."
+        exit 1
+      end
+      raise
+    end
+  end
+  procs = [block]
+  $benchmark_methods.reverse_each do |harness_name, harness_method|
+    prok = procs.pop
+    procs << proc { harness_method.bind(self).call(n, **kwargs, &prok) }
+  end
+  raise "Bad logic: #{procs.size}" unless procs.size == 1
+  result = procs.last.call
+  result || return_results([0], [1.0])
+end