[EUROCODE GRAPH] update burn in percentage to 0.5 (update test). delete test region eurocode. update eurocode graph.

[EUROCODE DATA] improve display for the eurocode return level graphs. rename linear margin temporal models.

[TEMPORAL LINEAR MARGIN][BAYESIAN ESTIMATION] modify fevd_fixed prior to ensure that prior is always applied on the shape parameter. add multiprocessing for eurocode return level uncertainty. add option to specify a last year for eurocode uncertainty computation.

[EUROCODE][DRAWING PER REGION] modify test region eurocode. add test_ gev temporal bayesian. add stationary version for the Bayesian. refactor utils at the root, to root_uils to avoid weird import issues.