Add jemalloc and use it including yjit, frozen_string in Dockerfile

Use `exec` in entrypoint.sh

docker/Dockerfile

@@ -1,10 +1,13 @@
-ARG RUBY_VERSION
-FROM ruby:$RUBY_VERSION-alpine
+ARG RUBY_VERSION=3
+FROM ruby:${RUBY_VERSION}-alpine
 
 ENV BUNDLE_PATH /usr/local/bundle/gems
 ENV LIB_PATH /var/grape
+ENV RUBYOPT --enable-frozen-string-literal --yjit
+ENV LD_PRELOAD libjemalloc.so.2
+ENV MALLOC_CONF dirty_decay_ms:1000,narenas:2,background_thread:true
 
-RUN apk add --update --no-cache make gcc git libc-dev gcompat && \
+RUN apk add --update --no-cache make gcc git libc-dev gcompat jemalloc && \
  gem update --system && gem install bundler
 
 WORKDIR $LIB_PATH

docker/entrypoint.sh

@@ -13,4 +13,4 @@ else
 fi
 
 # Keep gems in the latest possible state
-(bundle check || bundle install) && bundle update && bundle exec ${@}
+(bundle check || bundle install) && bundle update && exec bundle exec ${@}