Optimize ActiveRecord queries in User#next_unpassed_progression_level

[wjordan]

This PR optimizes User#next_unpassed_progression_level in script_levels#show, eliminating 3 DB queries from this high-scale route:

Reusing the user_levels_by_level query (cached by ActiveRecord Query Cache) removes:

SELECT user_levels.* FROM user_levels WHERE user_levels.user_id = [user] AND user_levels.script_id = [script] AND user_levels.level_id IN ([level_ids]) ORDER BY id desc

Using the script cache instead of user_level.level.script_levels.where(script_id: script.id).first removes:

• SELECT levels.* FROM levels WHERE levels.id = 455174957 LIMIT 1
• SELECT script_levels.* FROM script_levels INNER JOIN levels_script_levels ON script_levels.id = levels_script_levels.script_level_id WHERE levels_script_levels.level_id = [level] AND script_levels.script_id = [script] ORDER BY script_levels.id ASC LIMIT 1

Part of ActiveRecord query-optimization pass (see #18390). These queries combined account for ~9% of our current DB-query load.