added soma features (volume + working on best fitting ellipsoid axes) + modified skl brick.edge algo to support None value for calculus of edge lengths

issue with the use of ext_nfo['lmp'] solved by deleting 0s during the search of the ext uid with np.where(site>0)
now working on root storage in the graph/edge/node attributes

pb with ext_nfo["lmp"] which do not contain the connexion, making not possible its use for graphs and root extraction

+ nutrimorph.py setting

STEP1 of GRAPH EXTRACTION: Storage of adjacent extensions end points to somas into ext_root [[coord: tuple{3}, idx: int]]