Hello!

persist-defvar does not persist records or hash tables correctly.

Here's a minimal example with a hash table:

(progn
  (persist-defvar foo (make-hash-table :test #'equal) "docstring")
  (puthash 'bar t foo)
  (persist-save 'foo)
  (gethash 'bar (persist-default 'foo))) ;; Expected nil, got t

This patch fixes persisting records by using copy-tree. Currently,
copy-tree does not work with records (see
<https://lists.gnu.org/archive/html/bug-gnu-emacs/2023-05/msg00875.html>).
The following snippet will return the expected value only when both this
patch and the above-linked patch are applied:

(progn
  (cl-defstruct baz a)
  (persist-defvar quux (make-baz :a nil) "docstring")
  (setf (baz-a quux) t)
  (persist-save 'quux)
  (baz-a (persist-default 'quux))) ;; Expected nil, got t

Before applying this patch, the updated values in both cases are not
persisted to disk. With the patch, the updated values are persisted as
expected.

Best,

Joseph