default,locator: predicate takes ref to NodeRef

The predicate is more convenient for use in this form, because methods
such as `filter()` expect predicates to take values by reference.
It makes implementation in the following commit more elegant.
However, it unfortunately brings a breaking change.

Author: wprzytula

scylla/src/transport/load_balancing/default.rs

@@ -396,13 +396,13 @@ impl DefaultPolicy {
     fn make_rack_predicate<'a>(
         predicate: impl Fn(&NodeRef<'a>) -> bool + 'a,
         replica_location: ReplicaLocationCriteria<'a>,
-    ) -> impl Fn(NodeRef<'a>) -> bool {
+    ) -> impl Fn(&NodeRef<'a>) -> bool {
         move |node| match replica_location {
             ReplicaLocationCriteria::Any | ReplicaLocationCriteria::Datacenter(_) => {
-                predicate(&node)
+                predicate(node)
             }
             ReplicaLocationCriteria::DatacenterAndRack(_, rack) => {
-                predicate(&node) && node.rack.as_deref() == Some(rack)
+                predicate(node) && node.rack.as_deref() == Some(rack)
             }
         }
     }

scylla/src/transport/locator/mod.rs

@@ -244,19 +244,17 @@ impl<'a> ReplicaSet<'a> {
     pub fn choose_filtered<R>(
         self,
         rng: &mut R,
-        predicate: impl Fn(NodeRef<'a>) -> bool,
+        predicate: impl Fn(&NodeRef<'a>) -> bool,
     ) -> Option<NodeRef<'a>>
     where
         R: Rng + ?Sized,
     {
         let happy = self.choose(rng)?;
-        if predicate(happy) {
+        if predicate(&happy) {
             return Some(happy);
         }
 
-        self.into_iter()
-            .filter(|node_ref| predicate(node_ref))
-            .choose(rng)
+        self.into_iter().filter(predicate).choose(rng)
     }
 
     /// Gets the size of the set.