Add support for python dimacs reader in memory

[mtreinish]

Is your feature request related to a problem? Please describe.

Currently the read_dimacs_file method exposed through the python api requires a file path and works by opening the file. This puts an unnecessary constraint when using the api to write out a file to disk especially if the string is constructed in python this just seems unecessary.

Describe the solution you'd like

The dimacs parser being used supports passing in a dimacs file as an std::istream: https://lorina.readthedocs.io/en/latest/dimacs.html#_CPPv4N6lorina11read_dimacsERNSt7istreamERK13dimacs_readerP17diagnostic_engine

we can expose this via the python interface as a file like object (not sure how that connects with pybind11 but there should be a way). Ideally the interface would take either a file like object like a file, BytesIO,or a raw string we can pass to this.

Describe alternatives you've considered

The other alternative is just in pure python, basically adds a method that takes a stream or string and dumps it to a temp file and then we pass the temp file path to the existing read_dimacs, but doing it this way would just be shifting the current workaround from external to tweedledum to internal.

Additional context

[boschmitt]

Binding to istream seems to be complicated. I think that for the purposes of unit testing it should be enough to accept a string which contains the whole DIMACS. (I expect that the most common usage would actually be for passing the a file.)

I will work on this later, unless anyone else want to give it a try as a firs contribution to tweedledum.

[1ucian0]

+1 to support istream. It would be much easier in a demo to define the content of the file in a your jupyter notebook and then using it directly as StringIO.