Fix UserType response fields

[jychp]

Summary

• add the missing UserType response fields already present in the local OpenAPI schema
• preserve UserType(id=...) serialization for existing embedded user-type requests
• add focused coverage for UserType response deserialization

Source check

• No pull request template is present in this repository under .github
• UserType fields were taken from openapi/api.yaml and cross-checked against openapi/management.yaml
• The public Okta User Types API reference lists the same response fields

Validation

• .venv/bin/python -m pytest tests/test_user_type.py tests/integration/test_user_types_it.py
• git diff --check
• .venv/bin/python -m pytest: 599 passed, 44 skipped, 1 unrelated existing failure in test_header_mutation.py because the top-level async test is not marked for an async pytest plugin

Fixes #535