Avoid double sorting in max_fp and curve_max_fp

[pneuvial]

This looks very suboptimal:

https://github.com/pneuvial/sanssouci.python/blob/29e99a35eeea673eb4802fe9bf6ee4b12c49011b/sanssouci/post_hoc_bounds.py#L41-L44

• the sorting is done twice
• thr = thr[np.argsort(thr)] is probably more expensive than thr = np.sort(thr)

Is there any good reason not to replace the above lines by

thr = np.sort(thr)

?

[pneuvial]

No good reason found!

[pneuvial]

Will be addressed by #40