lexicons: pulls: pull rounds out into their own records #406

as discussed on discord here is a pull for the in progress pull related "atprotoation" lexicon changes! these arent quite yet ready so consider them a "draft" especially this top one as it does not include any implementation whatsoever. #402 and #403 i would consider ready for merge. in principle #404 and #405 are too but i think it would be wise to wait until #406 is done to merge those so we do all the bigger pr record changes all in one go.

i was thinking about the issue here more while trying to sleep as i tend to do and i think ive come to a kind of conclusion?

the main issue ive been having with trying to model the relationships here is that there is a one to one mapping between PR and change id. but we are also in a situation where resubmission can change the stack order and dependencies. i ended up realising that my pain came from trying to treat these two different things as if they are the same thing. so the idea i came up with is to put these two in the different places they belong: change id for the PR in the PR record and parent change/parent PR in the round/submission record.

i think thats the most logical solution even if it ends up spreading the stack info across more records. this might also be grounds for some changes in UI (to show it if a round has changed the stack relationship) but i think that can come later if wanted