refactor: Reserve memory in advance and move object instead of copying (

acts-project#3091)

as the title says. 

Most likely the second is not an issue since it's just a proxy ... but still it does not hurt

Core/include/Acts/TrackFinding/CombinatorialKalmanFilter.hpp

@@ -1189,6 +1189,7 @@ class CombinatorialKalmanFilter {
     }
 
     std::vector<typename TrackContainer::TrackProxy> tracks;
+    tracks.reserve(combKalmanResult.lastMeasurementIndices.size());
 
     for (auto tip : combKalmanResult.lastMeasurementIndices) {
       auto track = trackContainer.makeTrack();
@@ -1208,7 +1209,7 @@ class CombinatorialKalmanFilter {
 
       calculateTrackQuantities(track);
 
-      tracks.push_back(track);
+      tracks.push_back(std::move(track));
     }
 
     return tracks;