Fix #213: Add metadata to TorchExperiment._evaluate() method

[Lokkuchakreshkumar]

The metadata dictionary in TorchExperiment._evaluate() was always empty. This fix populates it with useful training information:

• num_epochs_trained: The number of epochs the model was trained for
• all_metrics: All metrics collected during training

This is consistent with other Hyperactive integrations (sklearn, sktime) which also return useful metadata.