Add ractor benchmark gvl_release_acquire.rb

Measures time taken to acquire and release the GVL over and over. Right
now it's quite a large overhead when we have a few ractors.

Author: luke-gruber

benchmarks/ractor/gvl_release_acquire.rb

@@ -0,0 +1,9 @@
+require_relative "../../harness/loader"
+
+run_benchmark(5) do |num_rs, ractor_args|
+  output = File.open("/dev/null", "wb")
+  input = File.open("/dev/zero", "rb")
+  100_000.times do
+    output.write(input.read(10))
+  end
+end