I dont remember the name of it, but there were tools that could store issues inside of git. It'd be hard to keep it in sync with everybody without a central repo, but maybe not much harder than keeping the code in sync too.
Lemmy is all public. There's no private timelines, so any 2way block would be superficial anyway right? A blocked user can just log out, or use a different account on a different instance. It'd give people a false sense of security if anyone said bidirectional blocking was a thing.
Something like Twitter could have bidirectional blocking because you can also make all of your posts private.
Without knowing the context... make sure you report people who truly are bullying. Some instances may not do anything, but a lot do care and don't tolerate bullying and harassment.
Are you sure you're not a machine?