Alias th used without importing torch in utils.eval_utils.py

[sintijas]

Description

The code uses the alias th to refer to torch in utils.eval_utils.py, specifically in the aggregate() function, but torch is not imported in the script.

Reproducing the error

Train the model with config["aggregation"] set to either one of ['concat', 'max', 'min'].
Observe the error:
Error: name 'th' is not defined

Suggested Fix

Add the following line at the beginning of the script:
import torch as th