[contrasting project] add global mean temperature data, and add test for adding these covariate to the coordinates.

[contrasting project] fix memory issue that was happening while loading many precipitation studies. issue #300

[EXTREME ESTIMATOR] refactor margin_fits folder. extreme estimator folder. and extreme_models folder

[COORDINATE] refactor starting year & df_temporal_coordinates. to normalize the same way any temporal covariate. So that each fit has the same type of normalized data as input. add multiple transformation.