bug#56623: memory leak introduced by new nonrecursive lisp reader

[Tom Gillespie]

While tracking down a memory leak in racket-mode git bisect
landed on b903507b36c438653a02d7b6291e9744d5221e28
Nonrecursive Lisp reader (bug#55676).

I do not have a minimal reproduction at the moment, but a
non-minimal one is documented at
see https://github.com/greghendershott/racket-mode/issues/632.
There are before and after graphs showing the change in behavior in
https://github.com/greghendershott/racket-mode/issues/632#issuecomment-1186609580

I have also attached the bisect script, and elisp needed to
reproduce the issue. Setting up the racket environment
to cause the issue is more involved (see the github issue).

Based on the behavior, it seems like strings and conses may be
marked by mark_lread but then somehow never unmarked, so
they never get collected, but that is a blind guess and I have no
idea if that is related at all.

ow.el
Description: Text Data

emacs-memory-leak-test.el
Description: Text Data

bisect-memory.sh
Description: application/shellscript