Committee error

[LarsSchaaf]

Committee error

This PR provides:

1. A mace calculator for using mace committees as a metric for model error
   • A list of mace models can be supplied to a given calculator. The calculator returns the variance between the predictions in energy in forces as a metric for the predicted model error.
   • This method has been tested for committees, consisting of mace models trained on different random train/validation splits.
2. A script for active learning using MD
   • As an example use case of the calculator a quick AL script is included. This simply runs MD until the predicted error reaches a set threshold.

[ilyes319]

Looks good to me! @LarsSchaaf Can you provide a test following the calculator https://github.com/ACEsuit/mace/blob/main/tests/test_calculator.py ?