Scan over strength of residual connections

In the track condensation network, scan over the strength of the residual connection `alpha_hc` (currently set to 0.5 by default). Example config:

```yaml
class_path: gnn_tracking.training.tc.TCModule
init_args:
  model:
    class_path: gnn_tracking.models.track_condensation_networks.GraphTCNForMLGCPipeline
    init_args:
      alpha_hc: 0.5
```