[ENH] Allow `-inf` scores in `scio.eval.ROC`

[eliegoudout]

Describe the proposed new feature or enhancement:

For simplicity, the current implementation leverages a lot the fact that with threshold = -inf, we have FP = TP = 0 as long as there no score equal to -inf.

It introduces a runtime constraint for no good theoretical reason.

Should be fixed in the future.