Extend sat_hardnesst struct to keep track of the actual clauses, not just number of clauses

Currently, solver hardness tracks number of clauses and not the actual clauses for an
instruction. This mapping will help identfy code hotspots based on which of the clauses
belong to the SAT core.
This commit extends the sat_hardnesst structure to include mapping between clauses and
ssa expression.

Author: Natasha Yogananda Jeppu

src/solvers/solver_hardness.h

@@ -50,6 +50,7 @@ struct solver_hardnesst
     size_t clauses = 0;
     size_t literals = 0;
     std::unordered_set<size_t> variables = {};
+    std::vector<std::vector<int>> clause_set = {};
 
     sat_hardnesst &operator+=(const sat_hardnesst &other);
   };