Clean up backup file and update .gitignore

Co-authored-by: jackfirth <[email protected]>

Author: Copilot

.gitignore

@@ -1,6 +1,7 @@
 compiled/
 doc/
 *~
+*.backup
 # These only come up if you generate the scribble docs manually, instead of
 # through `raco setup`. But we exclude them anyway to help newcomers (and
 # Copilot) avoid accidentally committing rendered documentation files.