[Diversity module] Adding tests for diversity measurements

[FanwangM]

We will need to add tests for the following function. Moreover, a wrapper function or Python class simplifies the usage of the diversity functions.

• total diversity column, Eq. 4 on page 843 of J. Chem. Inf. Comput. Sci. 1997, 37, 841-851 (the
  first method in this paper)
• Eq. 9 on page 844 of J. Chem. Inf. Comput. Sci. 1997, 37, 841-851 (the second method in this
  paper)
• Gini coefficient from Journal of Computational Chemistry2016,37, 2091–2097, Eq 12, 13 as well
• entropy from Eq. 9 on page 4 of Leguy et al. J Cheminform (2021) 13:76 with implementation at
  https://github.com/jules-leguy/EvoMol/blob/master/evomol/evaluation_entropy.py
• log-determinant function from Sci. Rep. 12: 1124 (2022)
• Wasserstein distance for property‑based evaluation of diversity. from Sci. Rep. 12: 1124
  (2022) with codes available at https://github.com/tomotomonakanaka/SUBMO
• Explicit Diversity Index from J. Chem. Inf. Model. 2006, 46, 5, 1898–1904

[FanwangM]

The tests have been added.