Device-code flow still uses concrete DeviceGrant when OAUTH2_PROVIDER_DEVICE_GRANT_MODEL is swapped

[diegopasqualin-beyond]

Describe the bug
When OAUTH2_PROVIDER_DEVICE_GRANT_MODEL points to a swapped DeviceGrant model, django-oauth-toolkit 3.2 device-code support is only partially compatible with that swap. Some code paths correctly use get_device_grant_model(), but important runtime paths still use the concrete oauth2_provider.DeviceGrant class directly.

This breaks the device flow because creation, lookup, and exception handling can target the wrong model/table or the wrong DoesNotExist exception class.

To Reproduce

1. Define a custom model subclassing oauth2_provider.models.AbstractDeviceGrant.
2. Set OAUTH2_PROVIDER_DEVICE_GRANT_MODEL to that swapped model.
3. Enable and exercise the device authorization flow.
4. Hit the device authorization endpoint so DOT creates a device grant.
5. Poll the token endpoint with grant_type=urn:ietf:params:oauth:grant-type:device_code.
6. Optionally test the browser confirmation/status views using the generated user code.

Concrete problematic paths observed in DOT 3.2:

• oauth2_provider.models.create_device_grant() uses DeviceGrant.objects.create(...)
• oauth2_provider.views.base.TokenView.device_flow_token_response() uses DeviceGrant.objects.get(...)
• oauth2_provider.views.device.DeviceGrantForm.clean_user_code() catches DeviceGrant.DoesNotExist instead of the swapped model's exception
• oauth2_provider.views.device.DeviceConfirmView and DeviceGrantStatusView use the concrete DeviceGrant model in lookups/views

Expected behavior
All device-grant runtime paths should consistently use get_device_grant_model() so swapped models are fully supported anywhere DOT creates, loads, or catches exceptions for DeviceGrant instances.

Version
3.2.x

• I have tested with the latest published release and it's still a problem.
• I have tested with the master branch and it's still a problem.

Additional context
I did a repo pass focused on DeviceGrant usages and found that some DOT code already handles swaps correctly, for example oauth2_provider.utils.set_oauthlib_user_to_device_request_user() and the objects.get(...) call in DeviceGrantForm. The bug appears to be incomplete migration to get_device_grant_model() rather than lack of swap support overall.

The likely fix is to replace concrete DeviceGrant usages in the affected runtime paths with get_device_grant_model() and add regression tests under swapped settings with a custom SampleDeviceGrant.

[diegopasqualin-beyond]

I'd be happy with either of the PRs being merged :)