Support 04-steiner properly

[ksk-jij]

Description

Steiner Tree Packing Problem contains too huge problems in terms of the number of variables. Thus, for now we don't convert all of the problems into ommx format but only small ones. However, once we need to do it, we should convert them into ommx. At that point, we need to convert them into ommx file. For now, we have the following three options to achieve that.

1. Write script in rust and use ommx rust SDK, which should be way faster than using python.
2. Support lp format by OMMX and directly use the given lp files to get ommx file.
3. Use Gurobi, SCIP or something else to create mps format from which OMMX can read it and produce ommx format, fromzpl.

Note

The information below could be useless, yet I'll leave them as a side note just in case.

• The current implementation to convert Steiner Tree Packing Problem is not direct transformation from zpl since zpl contains an if-else sentence, which is not available in jijmodeling.