Add e2e test for device deletion with connected users

[juan-malbeclabs]

The smart contract already prevents deleting a device that still has connected users by relying on the reference counter. However, this behavior is not yet validated in the end-to-end (e2e) test suite.

We need to extend the e2e tests to ensure:

• Devices with active user connections cannot be deleted.
• The reference counter is enforced correctly.
• Once all users are disconnected, device deletion succeeds.

Acceptance Criteria:

• Create an e2e test case that:
  1. Connects one or more users to a device.
  2. Attempts to delete the device and asserts the deletion fails with the expected error.
  3. Disconnects all users.
  4. Retries the deletion and asserts the device is successfully removed.
• Ensure the test runs reliably and covers both the fail and success scenarios.

Additional Notes:

• This test guarantees that the existing logic is preserved and prevents regressions.
• It complements unit tests by validating behavior at the integration level.