`pkgs.formats.toml` escapes backslashes and cannot emit raw control
characters, so key-binding `chars` written as escape text (e.g.
"\uXXXX" or the "\^[" caret form) ended up as invalid literals in the
generated config. Rewrite each escape to a placeholder before
generation and restore it to "\u" afterward.
Use `builtins.split` so escapes are handled anywhere in the value,
including when repeated or mixed with other text.
Austin Horstman
3d8f49f360