gptel-rewrite: Copy post-rewrite-functions to temp buffer

* gptel-rewrite.el (gptel--rewrite-callback): The buffer-local
value of `gptel-post-rewrite-functions' in the rewrite buffer is
not respected when the hook is called, because the hook is called
in the temporary buffer where the response is being collected.

Copy the buffer-local value of `gptel-post-rewrite-functions' to
the temporary buffer before calling the hook in
`gptel--rewrite-callback'.

Author: karthink

gptel-rewrite.el

@@ -514,6 +514,8 @@ INFO is the async communication channel for the rewrite request."
             (let ((inhibit-read-only t))
               (delete-region (point) (point-max))
               ;; Run post-rewrite-functions on rewritten text in its buffer
+              (setq-local gptel-post-rewrite-functions
+                          (buffer-local-value 'gptel-post-rewrite-functions buf))
               (with-demoted-errors "gptel-post-rewrite-functions: %S"
                 (run-hook-with-args 'gptel-post-rewrite-functions (point-min) (point-max)))
               (when (and (plist-get info :newline)