Refactor RedisCacheStoreProxy to unlearn everything about redis client details to make it less prone to bugs in the future

Let RedisCacheStoreProxy only know and assume things about
RedisCacheStore API. Don't let it know anything about the specific redis
client behind the scenes, that's the job of RedisCacheStore only, not
ours.

lib/rack/attack/store_proxy/redis_cache_store_proxy.rb

@@ -9,13 +9,16 @@ module Rack
         end
 
         def increment(name, amount, options = {})
-          # Redis doesn't check expiration on the INCRBY command. See https://redis.io/commands/expire
-          redis.with do |r|
-            count = r.pipelined do
-              r.incrby(name, amount)
-              r.expire(name, options[:expires_in]) if options[:expires_in]
-            end
-            count.first
+          # RedisCacheStore#increment ignores options[:expires_in].
+          #
+          # So in order to workaround this we use RedisCacheStore#write (which sets expiration) to initialize
+          # the counter. After that we continue using the original RedisCacheStore#increment.
+          if options[:expires_in] && !read(name)
+            write(name, 1, options)
+
+            1
+          else
+            super
           end
         end