[Suggestion] Associate variables with attempt id instead of entire splits file

Nobody has claimed this yet.

Currently, most runners have separate splits files for different variables in the same category. I'd like to suggest associating variables to the `` tag so runs with different variables can all coexist on the same file.

This would simplify splits file management for runners, and enable easier variable switching for folks who play multiple variables in a same category.

In the future, this could also allow for new comparison opportunities - runners could choose to compare against runs with some of the same variables as the current run, all of the same variables, all runs regardless of variables, etc. Total playtime in a certain set of variables could easily be compared to play time across all variables.

Associating variables with `` seems (on the surface) like a simple solution that could also easily retain backwards compatibility, and allow for the creation of a tool to combine splits files with different variables into the new format (though the latter would probably be a separate project).

Would love to hear thoughts on feasibility, other possible implementations with similar outcomes, etc.

Start by assessing how variables are currently associated with splits files and how the tag is represented. Define the compatibility and comparison behavior required for multiple variable sets in one file, then determine whether the proposed model is feasible before implementation.

Written by the indexing model from the issue text.