columns: enable toolbar scroll to top

Fixes: https://github.com/damus-io/notedeck/issues/969
Signed-off-by: William Casarin <jb55@jb55.com>

crates/notedeck_columns/src/column.rs

@@ -42,6 +42,18 @@ pub struct Columns {
     pub selected: i32,
 }
 
+/// When selecting columns, return what happened
+pub enum SelectionResult {
+    /// We're already selecting that
+    AlreadySelected(usize),
+
+    /// New selection success!
+    NewSelection(usize),
+
+    /// Failed to make a selection
+    Failed,
+}
+
 impl Columns {
     pub fn new() -> Self {
         Columns::default()
@@ -60,20 +72,25 @@ impl Columns {
     /// Select the column based on the timeline kind.
     ///
     /// TODO: add timeline if missing?
-    pub fn select_by_kind(&mut self, kind: &TimelineKind) {
+    pub fn select_by_kind(&mut self, kind: &TimelineKind) -> SelectionResult {
         for (i, col) in self.columns.iter().enumerate() {
             for route in col.router().routes() {
                 if let Some(timeline) = route.timeline_id() {
                     if timeline == kind {
                         tracing::info!("selecting {kind:?} column");
-                        self.select_column(i as i32);
-                        return;
+                        if self.selected as usize == i {
+                            return SelectionResult::AlreadySelected(i);
+                        } else {
+                            self.select_column(i as i32);
+                            return SelectionResult::NewSelection(i);
+                        }
                     }
                 }
             }
         }
 
         tracing::error!("failed to select {kind:?} column");
+        SelectionResult::Failed
     }
 
     pub fn add_new_timeline_column(