Add test case with similarity of 2 identical trees

[lpatiny]

I would expect that the similarity is 1 but I have the impression it is not the case.

[lpatiny]

Clearly this algorithm does not yield a value between 0 to 1 which may be confusing but I think it is the way the algorithm was designed.

[lpatiny]

Please migrate to this new code:

• https://github.com/mljs/spectra-processing/blob/main/src/x/__tests__/xMassCenterVectorSimilarity.test.ts
• https://github.com/mljs/spectra-processing/blob/main/src/xy/xyMassCenterVector.ts