Check that a comment-only elisp rewrite left the code unchanged

When you bulk-rewrite comments and docstrings in a large elisp config, check that no code changed. Read every top-level form with read in emacs --batch, replace each string with a placeholder (walk conses and vectors), prin1 the forms from the old and new files, and cmp the output. Comments vanish at read time, so an identical result means only strings and comments changed. If the elisp is embedded in a Nix '' string, replace ${...} interpolations with a valid placeholder before reading. A string placeholder inside another string breaks the reader, so use a bare symbol there. For the edits, use a Python script with (old, new) pairs that asserts each old string occurs exactly once. Raw triple-quoted strings keep a backslash before a quote, so do not end a pair with \".