Time series metrics fails with variable length timeseries

[fealho]

The LSTM classifier doesn't support variable length time series unless they are sorted from longest to shortest. Since we don't need ONNX compatibility, we can remove this restriction:

RuntimeError: lengths array must be sorted in decreasing order when enforce_sorted is True. You can pass enforce_sorted=False to pack_padded_sequence and/or pack_sequence to sidestep this requirement if you do not need ONNX exportability.