Add Task.processed_at.

dump/src/reader/v4/mod.rs

@@ -174,6 +174,8 @@ impl V4IndexReader {
                 }
 
                 if task.id as usize == index_metadata.creation_task_id {
+                    created_at = task.processed_at();
+
                     break;
                 }
             }

dump/src/reader/v4/tasks.rs

@@ -104,6 +104,13 @@ impl Task {
         })
     }
 
+    pub fn processed_at(&self) -> Option<OffsetDateTime> {
+        match self.events.last() {
+            Some(TaskEvent::Succeded { result: _, timestamp }) => Some(timestamp.clone()),
+            _ => None,
+        }
+    }
+
     pub fn updated_at(&self) -> Option<OffsetDateTime> {
         match self.events.last() {
             Some(TaskEvent::Created(ts)) => Some(*ts),