refactor: move the revision listing methods into a RevisionManager mixin (ROADMAP.md #73) (#93)

Author: pablospe

docx_editor/track_changes/base.py

@@ -142,3 +142,6 @@ def _rewrite_insert_at(self, paragraph, text_map: TextMap, char_pos: int, text:
 
     def _split_foreign_ins_at(self, edge_node, offset: int) -> Element | None:
         raise NotImplementedError
+
+    def changeset_id_of(self, group_id: int) -> int | None:
+        raise NotImplementedError