message: use extend_from_slice
diff: @@ -75,7 +75,7 @@ impl<'a> PandasColumnObject for StringColumn<'a> {
  impl<'a> PandasColumn<Bytes> for StringColumn<'a> {
  fn write(&mut self, val: Bytes) {
  self.string_lengths.push(val.len());
  - self.string_buf.extend(val);
  + self.string_buf.extend_from_slice(&val);
  self.try_flush();
  }
  }
  @@ -85,7 +85,7 @@ impl<'a> PandasColumn<Option<Bytes>> for StringColumn<'a> {
  match val {
  Some(b) => {
  self.string_lengths.push(b.len());
  - self.string_buf.extend(b);
  + self.string_buf.extend_from_slice(&b);
  self.try_flush();
  }
  None => {
  