Pending tests

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• models.Lasso
• diffusion.euler_explicit2D
• diffusion.euler_implicit_coef_mat
• diffusion.crank_nicolson_coef_mats
• diffusion.build_coef_mat
• diffuision.build_mat
• iterables.similarity
• spatial.equidist_polar
• spatial.neighbour_count
• spatial.get_boundaries
• plots.density
• plots.piano_consensus
• plots.venn
• plots.volcano
• plots.upset_wrap

[npalacioescat]

Worth checking matplotlib testing page for plots module

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To add also signal module and new plot functions (if possible)