Update mail.py to fetch mails in bulk

This speeds up the mail processing. See also https://github.com/paperless-ngx/paperless-ngx/discussions/5230

src/paperless_mail/mail.py

@@ -569,6 +569,7 @@ class MailAccountHandler(LoggingMixin):
                 criteria=criterias,
                 mark_seen=False,
                 charset=rule.account.character_set,
+                bulk=True
             )
         except Exception as err:
             raise MailError(