RPC Block Subscription (#21787)

* add stuff

* compiling

* add notify block

* wip

* feat: add blockSubscribe pubsub method

* address PR comments

Co-authored-by: Lucas B <buffalu@jito.network>
Co-authored-by: Zano <segfaultdoctor@protonmail.com>

runtime/src/bank.rs

@@ -1505,6 +1505,10 @@ impl Bank {
             .scan_results_limit_bytes
     }
 
+    pub fn proper_ancestors_set(&self) -> HashSet<Slot> {
+        HashSet::from_iter(self.proper_ancestors())
+    }
+
     /// Returns all ancestors excluding self.slot.
     pub(crate) fn proper_ancestors(&self) -> impl Iterator<Item = Slot> + '_ {
         self.ancestors