[Confidence Interval] use fix r.ci.fevd.mle_fixed for the Gumbel case in the Python code. fix the R code one more time for the gradient

[CONFIDENCE INTERVAL] in the non stationary case, only the normal method is defined. in the stationary, i managed to add test the "boot" method. But for the "proflik" method there was a crash in R related to the spline, that i did not resolve

[CONFIDENCE INTERVAL] add confidence interval test for the normal (i.e. delta) confidence interval method

[EXTREME ESTIMATOR] add test confidence interval. Add confidence interval with the ci method in the Bayesian case. add test for the stationary case. put the division by 100 (to get snow load) in eurocode vizualizer