Add utility to collect clauses and display the clause set in json output for write-solver-stats-to

Clauses are stored as a sorted vector of integers.

clang format solver_hardness.cpp

Author: Natasha Yogananda Jeppu

src/solvers/solver_hardness.cpp

@@ -26,8 +26,8 @@ operator+=(const solver_hardnesst::sat_hardnesst &other)
   clauses += other.clauses;
   literals += other.literals;
   variables.insert(other.variables.begin(), other.variables.end());
-  clause_set.insert(clause_set.end(),
-    other.clause_set.begin(), other.clause_set.end());
+  clause_set.insert(
+    clause_set.end(), other.clause_set.begin(), other.clause_set.end());
   return *this;
 }