Refresh layout of option lists on add.

Ensures options added to an empty list after mount are displayed.

Author: =

src/textual/widgets/_option_list.py

@@ -373,6 +373,7 @@ def add_options(self, new_options: Iterable[OptionListContent]) -> Self:
                 self._id_to_option[option._id] = option
             add_option(option)
         if self.is_mounted:
+            self.refresh(layout=True)
             self._update_lines()
         return self