DEV: enable frozen string literal on all files

This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.

Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging

lib/common_passwords/common_passwords.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # CommonPasswords will check a given password against a list of the most commonly used passwords.
 # The list comes from https://github.com/danielmiessler/SecLists/tree/master/Passwords
 # specifically the list of 10 million passwords, top 100k, filtered by length