feat: don't repartition for the sake of the metadata eraser (#2559)

The `MetadataEraserExec` is super lightweight and doesn't really justify
partitioning. I had a plan recently that was partitioning just for this
node and that seems wasteful.

rust/lancedb/src/table/datafusion.rs

@@ -85,6 +85,14 @@ impl ExecutionPlan for MetadataEraserExec {
         vec![&self.input]
     }
 
+    fn maintains_input_order(&self) -> Vec<bool> {
+        vec![true; self.children().len()]
+    }
+
+    fn benefits_from_input_partitioning(&self) -> Vec<bool> {
+        vec![false; self.children().len()]
+    }
+
     fn with_new_children(
         self: Arc<Self>,
         children: Vec<Arc<dyn ExecutionPlan>>,
@@ -486,7 +494,6 @@ pub mod tests {
         TestFixture::check_plan(
             plan,
             "MetadataEraserExec
-             RepartitionExec:...
              ProjectionExec:...
              LanceRead:...",
         )