fix(core): do not count disabled observers as stale (#7059)

* fix: do not notify the cache of `observerOptionsUpdated` if the prevOptions weren't defaulted

non-defaulted prev options indicate a "mount" event, in which case we don't want to fire an "update" event

* fix: react-query tests

with the new assumption that disabled observers are not stale

* fix: solid-query tests

with the new assumption that disabled observers are not stale

* fix: re-add check

accidentally removed to test a failing test

* fix: prefer the stale value of observers if one exists

that check looks for data not undefined anyways, but it also returns "fresh" for disabled observers now