Django-visitor-pass

* Add support for Django 5.0
* Add support for Python 3.11, 3.12
* Drop support for Django 3.1
* Replace isort, flake8 with ruff

* Add support for per-token session expiry (9)

* Return `HttpReponseBadRequest` (400) on malformed UUID token, h/t chrisapplegate, issue 7

* Add support for self-service tokens

* Add `Visitor.expires_at` timestamp to manage expiry
* Add `Visitor.is_active` switch to allow instant disabling of visitor passes
* Add `Visitor.validate()` method to validate pass
* Add `VISITOR_TOKEN_EXPIRY` setting (default: 300s)
* Add `VISITOR_SESSION_EXPIRY` settings (default: 0s - expires on browse close)