Improves performance by keying every chunk thats part of a structure to a hashmap
instead of only the first one.
This allows us to avoid iterating the entire structures value set to see
if a block position is inside of a structure.
This should have pretty decent performance improvement to any standard world
that has been around for a whilewith lots of structures due to ineffeciencies
in how MC stores structures (even unloaded chunks has structured data loaded)
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