Peerset cleanup (#6078)

* Move methods from Peerset to peers structs

* Remove priority_only from peersstate

* Refactor PSM

* Don't test private fields

* Update sc_network

* Remove wrong comment

* Also fix small stupidity when setting reserved_only

* Put back priority_group

* Restore priority groups as before

* Apply suggestions from code review

Co-authored-by: André Silva <[email protected]>

* Do the reserved only change

* Update client/peerset/src/lib.rs

Co-authored-by: Arkadiy Paronyan <[email protected]>

* Use HashSet::difference

Co-authored-by: André Silva <[email protected]>
Co-authored-by: Arkadiy Paronyan <[email protected]>