fix(positioner box): include username in scan queue request

[wakonig]

Description

Minor patch for compatibility with user-scope scan queue requests, cf. bec-project/bec#725

Definition of Done

• Documentation is up-to-date.

[Copilot]

Pull request overview

This PR updates the scan_queue_request API call to include the username parameter, aligning with changes in the upstream BEC library (PR #725) to support user-scoped scan queue requests.

• Updated _stop_device method to pass self.client.username to MessageEndpoints.scan_queue_request()
• Updated corresponding unit test to verify the username parameter is correctly passed

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
bec_widgets/widgets/control/device_control/positioner_box/_base/positioner_box_base.py	Modified the _stop_device method to include self.client.username parameter in the scan queue request call
tests/unit_tests/test_positioner_box.py	Updated test assertion to verify the username parameter is correctly passed to the scan queue request endpoint

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[Copilot]

The mocked_client used in this test does not explicitly set a username attribute. While MagicMock will auto-generate it, consider adding an explicit username to the mocked_client fixture to make the test more realistic and ensure it properly validates the username parameter is being passed correctly.