Convert TimelineDelegate to cpp

There are 2 main reason for doing this:
1. Because I can, I wanted to see if I could do it
2. It gets rid of the janky qml re parenting stuff so should be faster.

src/timeline/LoadingDelegate.qml

@@ -5,8 +5,16 @@ import QtQuick
 
 import org.kde.kirigami as Kirigami
 
+import org.kde.neochat
+
 TimelineDelegate {
     id: root
+
+    width: parent?.width
+    rightPadding: Config.compactLayout && root.ListView.view.width >= Kirigami.Units.gridUnit * 20 ? Kirigami.Units.gridUnit * 2 + Kirigami.Units.largeSpacing : Kirigami.Units.largeSpacing
+
+    alwaysFillWidth: Config.compactLayout
+
     contentItem: Kirigami.PlaceholderMessage {
         text: i18n("Loading…")
     }