Text editor: undo and redo the last ten edits

Context

Welcome to the notes app team. The editor in editor/ handles typing, backspace, the cursor, and copy and paste (levels 1 and 2), and its tests pass. Users now want undo and redo. The two methods are stubbed in editor/text_editor.py, and the rules for level 3 are in README.md.

Build level 3 in 35 minutes. The checks are graded one by one, so each part you get working counts even if the rest is not done.

EDIT-3: Undo and redo (level 3)

Acceptance criteria

• undo takes back the latest edit (insert, delete or paste that changed the text), putting back both the text and the cursor as they were just before it.
• redo brings back the edit undone most recently, with the text and cursor as they were just after it.
• Moving the cursor, copying, and calls that changed nothing are not edits, so undo skips them.
• A new edit ends redo.
• Only the last 10 edits can be undone.
• With nothing to undo or redo, nothing changes.
• Levels 1 and 2 keep working.

Notes

• Run pytest tests/visible. tests/visible/test_level3.py fails until level 3 works.
• Practice task modelled on candidate reports of text editor undo and redo rounds at Microsoft and Amazon. Original StackYard code, not the actual question; not affiliated with Microsoft or Amazon.