feat: Add new data cells for discordant variant information

[jarbesfeld]

Two new statistics were added to the paper, and this PR contains two new cells in the mapping_analysis.ipynb notebook to compute these statistics:

1. The number of score sets without any discordant variants. The total number of concordant variant pairs across these score sets was then counted.
2. The number of score sets where the MAVE target sequence and human reference sequence were equivalent. For experiment 97, we took the mapped protein variants that were provided by the submitter, so these score sets were added by default. Given score sets where the MAVE target sequence and human reference sequence are equivalent, we would expect the VRS IDs to be equivalent as the same variations are being described on the same sequence.