EpitopeAssemblyWithSpacer with Cbc fails for more than 14 peptides

[mattheiter]

Cbc crashes for larger instances of the ILP for spacer design. Here's a minimal example that will crash after ~4 mins:

cleavage_predictor = CleavageSitePredictorFactory("PCM")
epitope_predictor = EpitopePredictorFactory("BIMAS")

opti_result = EpitopeAssemblyWithSpacer(
        peptides,
        cleavage_predictor,
        epitope_predictor,
        supported_alleles,
        solver="cbc",
        verbosity=1
    ).solve()

Please consider the log output.

Besides the crash, the python process also doesn't terminate since the crashed thread seems to be stuck. I tried to fix the problem by catching the exception and explicitly closing/terminating the thread pool but that didn't fix the problem either.