Add initializer for yjit from Rails 8 (#24)

Reviewed-on: #24

config/initializers/yjit.rb

@@ -0,0 +1,12 @@
+# Automatically enable YJIT if running Ruby 3.3 or newer,
+# as it brings very sizeable performance improvements.
+# Many users reported 15-25% improved latency.
+
+# If you are deploying to a memory-constrained environment,
+# you may want to delete this file, but otherwise, it's free
+# performance.
+if defined? RubyVM::YJIT.enable
+  Rails.application.config.after_initialize do
+    RubyVM::YJIT.enable
+  end
+end