Fix mcsat conflict analysis
Fix mcsat conflict analysis

When analyzing an mcst conflict clause and looking at a semantic
propagation in the trail, the last resolved clause was looked at again,
which caused an invalid history to be generated (the computation of the
backtrack clause was not affected because the second resolution of the clause
was basically a no-op thanks to the 'seen' field), thus it did not
introduce any soundness bug, just a faulty clause history which was
caught during proof expansion.

Gbury/mSAT