Compute per-client and global metrics and losses.
This objective computes several metrics of interests based on FLamby losses
and Flamby metrics per dataset and globally.
This way we can compare per-dataset metric vs averaged metrics across
datasets and global metric when datasets are pooled.
The objective_value is the average train or test loss across datasets
this depends on wether we use the validation datasets or the test
ones.
Parameters
----------
BaseObjective : BaseObjective
The base objective in BenchOpt