Achievements in Core Sets Filter is Not Working

[isaacschepp]

Describe the bug

https://retroachievements.org/achievementList.php?s=14&p=3

The achievement in core sets filter is not working on the "Hardest Achievments" page.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://retroachievements.org/achievementList.php?s=14&p=2
2. Click on Achievements in Core Sets
3. See that achievements from subsets are still included.

Expected behavior
It should filter out achievements in subsets.

Desktop (please complete the following information):

• OS: Windows 11 Home
• Browser: Chrome
• Version: Version 123.0.6312.105 (Official Build) (64-bit)

[wescopeland]

At present time, with some minor nuance, subsets are functionally equivalent to core sets on the site.

We should revisit this issue while building out the new multiset functionality. I'd prefer not to build a workaround into the current system for handling this specific logic until we're closing to multiset being a reality. Right now the only way to check if a set is a subset is by using string comparisons in a game's title. Unfortunately, this disables indexing.