SAR-286 Migrate `AssignResources` to async/long running

src/ska_tango_base/base/base_device.py

src/ska_tango_base/base/task_queue_manager.py

src/ska_tango_base/subarray/reference_component_manager.py

src/ska_tango_base/subarray/subarray_device.py

tests/conftest.py

tests/long_running_tasks/test_multi_device.py

tests/long_running_tasks/test_reference_base_device.py

tests/long_running_tasks/test_task_queue_manager.py

tests/test_subarray_device.py