Scanning for usb cameras blocks main thread

[rodja]

With the new unified cameras (see #25) the scanning for usb devices is not async and hence blocks the main thread:

rosys_1     | 2023-12-16 06:54:24.929 [WARNING] asyncio/runners.py:118: Executing <Task pending name='UsbCameraProvider.update_device_list' coro=<_repeat_one_handler() running at /app/rosys/rosys.py:213> wait_for=<Future pending cb=[Task.task_wakeup()] created at /usr/local/lib/python3.11/asyncio/tasks.py:634> cb=[_handle_task_result() at /app/nicegui/background_tasks.py:50, set.discard()]> took 0.279 seconds
rosys_1     | 2023-12-16 06:54:34.987 [WARNING] asyncio/runners.py:118: Executing <Task pending name='UsbCameraProvider.update_device_list' coro=<_repeat_one_handler() running at /app/rosys/rosys.py:213> wait_for=<Future pending cb=[Task.task_wakeup()] created at /usr/local/lib/python3.11/asyncio/tasks.py:634> cb=[_handle_task_result() at /app/nicegui/background_tasks.py:50, set.discard()]> took 0.280 seconds
rosys_1     | 2023-12-16 06:54:45.019 [WARNING] asyncio/runners.py:118: Executing <Task pending name='UsbCameraProvider.update_device_list' coro=<_repeat_one_handler() running at /app/rosys/rosys.py:213> wait_for=<Future pending cb=[Task.task_wakeup()] created at /usr/local/lib/python3.11/asyncio/tasks.py:634> cb=[_handle_task_result() at /app/nicegui/background_tasks.py:50, set.discard()]> took 0.280 seconds
rosys_1     | 2023-12-16 06:54:55.061 [WARNING] asyncio/runners.py:118: Executing <Task pending name='UsbCameraProvider.update_device_list' coro=<_repeat_one_handler() running at /app/rosys/rosys.py:213> wait_for=<Future pending cb=[Task.task_wakeup()] created at /usr/local/lib/python3.11/asyncio/tasks.py:634> cb=[_handle_task_result() at /app/nicegui/background_tasks.py:50, set.discard()]> took 0.281 seconds
rosys_1     | 2023-12-16 06:55:05.112 [WARNING] asyncio/runners.py:118: Executing <Task pending name='UsbCameraProvider.update_device_list' coro=<_repeat_one_handler() running at /app/rosys/rosys.py:213> wait_for=<Future pending cb=[Task.task_wakeup()] created at /usr/local/lib/python3.11/asyncio/tasks.py:634> cb=[_handle_task_result() at /app/nicegui/background_tasks.py:50, set.discard()]> took 0.276 seconds
rosys_1     | 2023-12-16 06:55:15.154 [WARNING] asyncio/runners.py:118: Executing <Task pending name='UsbCameraProvider.update_device_list' coro=<_repeat_one_handler() running at /app/rosys/rosys.py:213> wait_for=<Future pending cb=[Task.task_wakeup()] created at /usr/local/lib/python3.11/asyncio/tasks.py:634> cb=[_handle_task_result() at /app/nicegui/background_tasks.py:50, set.discard()]> took 0.281 seconds
rosys_1     | 2023-12-16 06:55:25.186 [WARNING] asyncio/runners.py:118: Executing <Task pending name='UsbCameraProvider.update_device_list' coro=<_repeat_one_handler() running at /app/rosys/rosys.py:213> wait_for=<Future pending cb=[Task.task_wakeup()] created at /usr/local/lib/python3.11/asyncio/tasks.py:634> cb=[_handle_task_result() at /app/nicegui/background_tasks.py:50, set.discard()]> took 0.277 seconds
rosys_1     | 2023-12-16 06:55:35.226 [WARNING] asyncio/runners.py:118: Executing <Task pending name='UsbCameraProvider.update_device_list' coro=<_repeat_one_handler() running at /app/rosys/rosys.py:213> wait_for=<Future pending cb=[Task.task_wakeup()] created at /usr/local/lib/python3.11/asyncio/tasks.py:634> cb=[_handle_task_result() at /app/nicegui/background_tasks.py:50, set.discard()]> took 0.279 seconds
rosys_1     | 2023-12-16 06:55:45.276 [WARNING] asyncio/runners.py:118: Executing <Task pending name='UsbCameraProvider.update_device_list' coro=<_repeat_one_handler() running at /app/rosys/rosys.py:213> wait_for=<Future pending cb=[Task.task_wakeup()] created at /usr/local/lib/python3.11/asyncio/tasks.py:634> cb=[_handle_task_result() at /app/nicegui/background_tasks.py:50, set.discard()]> took 0.287 seconds