DEV: use Discourse.cache over Rails.cache

Discourse.cache is a more consistent method to use and offers clean fallback
if you are skipping redis

This is part of a larger change that both optimizes Discoruse.cache and omits
use of setex on $redis in favor of consistently using discourse cache

Bench does reveal that use of Rails.cache and Discourse.cache is 1.25x slower
than redis.setex / get so a re-implementation will follow prior to porting

spec/components/cache_spec.rb

@@ -9,6 +9,11 @@ describe Cache do
     Cache.new
   end
 
+  it "supports float" do
+    cache.write("float", 1.1)
+    expect(cache.read("float")).to eq(1.1)
+  end
+
   it "supports fixnum" do
     cache.write("num", 1)
     expect(cache.read("num")).to eq(1)