Fix Entropy Calculation

[xindizhang]

Fix Entropy Calculation

• Before: calculate entropy and average entropy across folds
• Now: calculate averaged probability distribution and calculate entropy based on ensemble probability

[GFJHogue]

Thanks @xindizhang!
I ended up moving the entropy calculations to use PyTorch's built-in torch.Categorical.entropy() implementation for i) a stronger guarantee of correctness and ii) less computational error for probabilities near-zero.
I also added type-hints to make future debugging easier.

In my own testing, all probability outputs are identical to v3.0.1 (good) and entropy values between Xindi's suggested code vs. my update to use torch.Categorical.entropy() match to 6 decimal places (also good).