Changes

fix: attribute issues (#3193)

* fix: NPEs from attribute related stuff

* chore: clarify comment

* fix: issues when using attribute key as argument

Changes:
Added argument parsing backward compatibility for /npc attribute command but also introduces more time cost (although it might be not so long, so we can assume it as zero)
Make OptionalAttributeCompletions return attribute keys for now as old enum names are too legacy.

* fix: rewrite attribute trait load logic
 (commit: 0239d5c)