Whether a metric is lower-is-better (an error/loss metric). The check is
case-insensitive and trims surrounding whitespace, so callers can pass a raw
metric name or a pre-lower-cased key interchangeably.
Parameters
metricKey: string
the metric name (e.g. RMSE, rmse, roc_auc)
Returns boolean
true for error metrics (RMSE/MAE/MSE/loss/logloss), else false
Whether a metric is lower-is-better (an error/loss metric). The check is case-insensitive and trims surrounding whitespace, so callers can pass a raw metric name or a pre-lower-cased key interchangeably.