replace HybridSet with NoteUnits

This will unify the collections that hold the notes to timelines
and threads and allow the notifications timeline to have grouped
notifications, among other things

Signed-off-by: kernelkind <kernelkind@gmail.com>

crates/notedeck_columns/src/actionbar.rs

@@ -385,7 +385,7 @@ pub fn process_thread_notes(
             created_at,
         };
 
-        if thread.replies.contains(&note_ref) {
+        if thread.replies.contains_key(&note_ref.key) {
             continue;
         }