Index map issue with nested strings

[misode]

This needs to be investigated

summon cow ~ ~ ~ {CustomName:'{"text":"hello","hoverEvent":{"action":"show_item","value":"{id:\'acacia_boat\'}"}}'}

[misode]

I found another case where it went wrong: Interestingly, it works correctly when using only double quotes:

[TheAfroOfDoom]

from https://github.com/SpyglassMC/Spyglass/pull/1355#issue-2365408905

this is a log of index maps when the core.string parser (?) is called.

you can see that at some point it's not actually receiving/merging with the old index map properly. i think it should be an ~easy-ish fix just need to figure out exactly where to connect prior index maps to the new one