Allow infinities instead of NaN to signify "goal has no target at this time step"
Would it be a good idea to allow the use of +/- infinity to signify that no target_min/max should be set at certain time? Currently we only allow the use of NaN for this, but NaN is very annoying in that any comparisons/arithmetic fails (whereas it typically behaves nicely with infinity). Something simple as
assert target_min.values <= target_max.values will fail if there are NaNs present.
As far as implementation is concerned, it seems that there are only some validation checks preventing the use of infinities as this. The generated constraint+objective is exactly equal for both NaN and +/- inf. There might be other changes needed, but first I just want to check if anyone else thinks this might be worth supporting.
Somewhat related to #1079 (closed)
 Two checks I could find was that target should be in the function range (which infinity obviously is not), and the monotonicity check.