Allow filter with join about walkable

[myguidingstar]

should not separate join-filters from filters, instead allow join filters as a new kind of filters so they can be combined freely (with and, or)

[myguidingstar]

the above example becomes:

{[(:person/all {:filters {;; in-table filter
                          :person/number [:> 0]
                          ;; join filter
                          :person/pets {:pet/yob [:> 1999]}}})]
 [:person/name :person/yob]}

[myguidingstar]

• extract the function that generates the above sub query (the SELECT inside an IN)
  • should also have sql query and params separated
• modify the filter spec to include join filters
• modify the WHERE emitter to include params introduced by sub queries