Previously cached counting made redis calls in main thread and performed
the flush in main thread.
This could lead to pathological states in extreme heavy load.
This refactor reduces load and cleans up the interface
Previously we were calling `EXPIRE` every time we incremented a given key. Instead, we can call EXPIRE once when the key is first populated. A LUA script is used to make this as efficient as possible.
Consumers of this Concern use daily keys. Since we're now calling EXPIRE only at the beginning of the day, rather than throughout the day, the expire time has been increased from 3 to 4 days.
This change both speeds up specs (less strings to allocate) and helps catch
cases where methods in Discourse are mutating inputs.
Overall we will be migrating everything to use #frozen_string_literal: true
it will take a while, but this is the first and safest move in this direction
