fix: ensure backend check correctly raises exception when not set

[robberwick]

This pull request includes changes to the BlinkStick client in src/blinkstick/clients/blinkstick.py and its corresponding tests in tests/clients/test_blinkstick.py. The most important changes include updating the backend check in the __getattribute__ method and modifying the test for methods requiring a backend.

Backend check update:

• src/blinkstick/clients/blinkstick.py: Changed the backend check in the __getattribute__ method to use getattr for better attribute handling.

Test modifications:

• tests/clients/test_blinkstick.py: Modified the test_all_methods_require_backend test to directly instantiate BlinkStick without using a mock or passing a device, ensuring that all methods raise an exception when the backend is not set.

[Copilot]

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