introduced new metis partitioning options

[paulheinr]

The goal of METIS is to partition a network in such a way that the number of cut edges is minimized. If edge weights are set, it minimizes the sum of the weights.
You can also explicitly assign node weights (multiple of them) that constrain the partitioning problem. Additionally, there is a tolerance factor regarding the constraints in which the results are allowed to lie.
See: https://www.lrz.de/services/software/mathematik/metis/metis_5_0.pdf

This PR introduces new partitioning options to qsim. The struct MetisOptions holds them. It consists of

• vertex_weight which holds predefined weight options
• edge_weight which can be turned on to use capacity as edge weight
• imbalance_factor which is the allowed relative weight difference in comparison to equal distribution of weight among the partitions

[Janekdererste]

Nice work!