Memoize relative_url for performance gains

[MaxLap]

My 250 pages site has a sidebar which links to every/most pages. I was tired to building the site taking so long, so after a bit of profiling, I noticed that #relative_url isn't memoized. So every link needs to rebuild the same relative urls.

Memoizing with the following in my config/initializers.rb made my build time go from 10s to 5s.

module MemoizeRelativeUrl
  def relative_url
    @relative_url ||= super
  end
end
Bridgetown::Resource::Base.prepend(MemoizeRelativeUrl)

I don't know if a relative_url is meant to change over the course of a build, but if it isn't, this is a massive usability improvement for me.

I don't know if the change should be on Bridgetown::Resource::Base or Bridgetown::Resource::Destination or somewhere else, but I think there should definitely be memoization somewhere.