[refactor] refactor one fold fit, enable to get sorted estimators with other selection criterion without more computation

[refactor] rename function from fit to margin function from fit. remove sorted_estimators_with_stationary

[projection snowfall] refactoring & move folders. adapt the relative change formula for negative values.activate the goodness of fit test. handle an additional type of climate coordinates. and plot of the value & of the GEV parameters.

[projection snowfall] fix one special case for the formula. fix issue in model check in one fold fit. fix the parameter for one model. big bug fix in evgam.

[projection snowfall] add climate_coordinates_with_effects attributes everywhere. refactor __init__ method for many temporal model.

[projection snowfall] fix error in one fold fit for the temperature covariate & for the significance.
modify number of parameters for the spline, and only counts the number of coefficients and not the number of knots.

[projection snowfall] modify altitude_class to altitude_group in visualizer_for_projection_ensemble.py. fix index for ensemble dataset.  add plot_relative_change_in_return_level.py

[projection snowfall] add functions_utils.py. modify one_fold_fit.py so that it may support one altitude fit.

[projection snowfall] adapt the one_fold_fit.py code to handle fit with a single altitude. Modify altitude_class by altitude_group, adapt tests. Modify the DefaultAltitudeGroup. adapt main_projections_ensemble.py

[projection snowfall] refactor first_year and last_year in OneFoldFit. and apply the code to check the difference in spatial patterns between safran 2020 reanalysis and ADAMont v2

[projection snowfall] add main_sensitivity_one_altitude_range.py. add detail plot for each massif for the return level

[projection snowfall] add preliminary analysis for the work on model with effect related to the GCM or RCM type.

[projection snowfall] improve one_fold_fit_merge.py. improve interval for the sensitivity plot. Add is_temperature_interval and is_shift_interval to define the intervals.

[refactor] fix issue. the temporal covariate is the the anomaly of temperature smoothed with a spline

[refactor] rename folders for one/two fold fit. move the code for the anomaly into temperature_covariate.py