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
* Cuts number of queries from 273 to 89
* Add some specs
* For a table with 500 posts, benchmarks locally shows a runtime
reduction from 0.046929135 to 0.032694705.
Régis Hanol
Sam Saffron
Guo Xiang Tan