custom BEC component to replace the need for run_subs
- separation between classification (Kind) and readout (Component)
- custom BEC-specific component with additional fields:
- signal_type: 'progress', 'file_event', 'dynamic_signals', 'preview', 'async_readback'
- ndims: int, optional but required for 'preview' signal_type
- custom BEC-specific signals for progress, file_event