refactor: move the insert and paragraph-split methods into a RevisionManager mixin (ROADMAP.md #73) (#92)

* refactor: move the insert and paragraph-split methods into a RevisionManager mixin (ROADMAP.md #73)

* test: cover the insert edge cases moved in ROADMAP.md #73 step 7

Author: pablospe

docx_editor/track_changes/base.py

@@ -136,3 +136,9 @@ def _ins_identity_attrs(self, ins_elem) -> str:
 
     def _adopt_split_tail(self, original_ins, new_nodes) -> None:
         raise NotImplementedError
+
+    def _rewrite_insert_at(self, paragraph, text_map: TextMap, char_pos: int, text: str) -> None:
+        raise NotImplementedError
+
+    def _split_foreign_ins_at(self, edge_node, offset: int) -> Element | None:
+        raise NotImplementedError