Rename num_entities to entity_count (#19781)

As discussed in
https://github.com/bevyengine/bevy/pull/19780#issuecomment-2994554024.

crates/bevy_app/src/app.rs

@@ -1582,7 +1582,7 @@ mod tests {
         app.add_systems(EnterMainMenu, (foo, bar));
 
         app.world_mut().run_schedule(EnterMainMenu);
-        assert_eq!(app.world().num_entities(), 2);
+        assert_eq!(app.world().entity_count(), 2);
     }
 
     #[test]

crates/bevy_ecs/src/lib.rs

@@ -1637,7 +1637,7 @@ mod tests {
 
         assert_eq!(q1.iter(&world).len(), 1);
         assert_eq!(q2.iter(&world).len(), 1);
-        assert_eq!(world.num_entities(), 2);
+        assert_eq!(world.entity_count(), 2);
 
         world.clear_entities();
 
@@ -1652,7 +1652,7 @@ mod tests {
             "world should not contain sparse set components"
         );
         assert_eq!(
-            world.num_entities(),
+            world.entity_count(),
             0,
             "world should not have any entities"
         );

crates/bevy_ecs/src/observer/mod.rs

@@ -727,7 +727,7 @@ mod tests {
         world.spawn(A).flush();
         assert_eq!(vec!["add_2", "add_1"], world.resource::<Order>().0);
         // Our A entity plus our two observers
-        assert_eq!(world.num_entities(), 3);
+        assert_eq!(world.entity_count(), 3);
     }
 
     #[test]

crates/bevy_ecs/src/system/commands/mod.rs

@@ -2342,7 +2342,7 @@ mod tests {
             .spawn((W(1u32), W(2u64)))
             .id();
         command_queue.apply(&mut world);
-        assert_eq!(world.num_entities(), 1);
+        assert_eq!(world.entity_count(), 1);
         let results = world
             .query::<(&W<u32>, &W<u64>)>()
             .iter(&world)

crates/bevy_ecs/src/world/command_queue.rs

@@ -423,12 +423,12 @@ mod test {
         let mut world = World::new();
         queue.apply(&mut world);
 
-        assert_eq!(world.num_entities(), 2);
+        assert_eq!(world.entity_count(), 2);
 
         // The previous call to `apply` cleared the queue.
         // This call should do nothing.
         queue.apply(&mut world);
-        assert_eq!(world.num_entities(), 2);
+        assert_eq!(world.entity_count(), 2);
     }
 
     #[expect(
@@ -462,7 +462,7 @@ mod test {
         queue.push(SpawnCommand);
         queue.push(SpawnCommand);
         queue.apply(&mut world);
-        assert_eq!(world.num_entities(), 3);
+        assert_eq!(world.entity_count(), 3);
     }
 
     #[test]

crates/bevy_ecs/src/world/mod.rs

@@ -220,7 +220,7 @@ impl World {
     ///
     /// This is helpful as a diagnostic, but it can also be used effectively in tests.
     #[inline]
-    pub fn num_entities(&self) -> u32 {
+    pub fn entity_count(&self) -> u32 {
         self.entities.len()
     }
 

crates/bevy_pbr/src/cluster/mod.rs

@@ -535,12 +535,12 @@ pub fn extract_clusters(
             continue;
         }
 
-        let num_entities: usize = clusters
+        let entity_count: usize = clusters
             .clusterable_objects
             .iter()
             .map(|l| l.entities.len())
             .sum();
-        let mut data = Vec::with_capacity(clusters.clusterable_objects.len() + num_entities);
+        let mut data = Vec::with_capacity(clusters.clusterable_objects.len() + entity_count);
         for cluster_objects in &clusters.clusterable_objects {
             data.push(ExtractedClusterableObjectElement::ClusterHeader(
                 cluster_objects.counts,