refactor(types): make queryKey required on ObserverOptions (#6879)

* refactor(types): make queryKey required on ObserverOptions

we cannot create an observer without a key, because an observer, per definition, watches a certain query by its key

* test: observers need a key

* chore: remove a branch that can't exist

we can't have an observer without a queryKey

* fix: when comparing with shallowEqualObjects, the currentResult must come first

because it doesn't detect length changes

* test: we get another event

* types: you can't set queryKey as default

* a test for undefined queryKey makes no sense

* fix: more type issues

* types: queryKey is also not required for defaultOptions in solid

* fix(core): shallowEqualObjects should return false for objects with different lengths

as we use it for options, and the length of options can change