refactor(operator): added updatePreconditioner method

the preconditioner must be built once before the solver begins to iterater, by putting the logic for this in a dedicated method it becomes cleaner to call

src/poly/utils/public/operator.h

@@ -99,4 +99,5 @@ private:
 private:
     void updateInverseNonlinearJacobian(const mfem::Operator &grad) const;
     void updateInverseSchurCompliment() const;
+    void updatePreconditioner(const mfem::Operator &grad) const;
 };