Display all users which used the current regcode.

I think, that we can ignore the patch from comment #25, because it adds changes from #3227667 → issue, so one can use one patch for implementing both features.
Attaching interdiff.

Could the new regcode_user table have a primary key?

I ran into this issue:
MYSQL READ-COMMITTED
For this to work correctly, all tables must have a primary key. The following table(s) do not have a primary key: regcode_users. See the setting MySQL transaction isolation level page for more information.

Drupal 9.5.8
php8.1

Added primary key to regcode_user table

The MR doesn't apply any longer, and is going to need manual rebasing. As long as that has to be done, lets do it for the current 2.0.x branch. This will require a new MR most likely.

created new MR for 2.0.x branch https://git.drupalcode.org/project/regcode/-/merge_requests/15 and pushed changes there