Apply suggestions from code review

Co-authored-by: Oleks V <comphead@users.noreply.github.com>

Author: alamb

datafusion/datasource/src/memory.rs

@@ -426,15 +426,7 @@ impl DataSource for MemorySourceConfig {
             }
             DisplayFormatType::TreeRender => {
                 let total_rows = self.partitions.iter().map(|b| b.len()).sum::<usize>();
-                let total_bytes = self
-                    .partitions
-                    .iter()
-                    .map(|b| {
-                        b.iter()
-                            .map(|batch| batch.get_array_memory_size())
-                            .sum::<usize>()
-                    })
-                    .sum::<usize>();
+                let total_bytes: usize = self.partitions.iter().flatten().map(|batch| batch.get_array_memory_size()).sum();
                 writeln!(f, "format=memory")?;
                 writeln!(f, "rows={total_rows}")?;
                 writeln!(f, "bytes={total_bytes}")?;