fix(poly): fixed -M bug in form

MFEM MixedVectorWeakDivergenceIntegrator is actually already -M in our derivation, I have negated this so that Mform -> M directly

src/poly/utils/public/operator.h

@@ -26,7 +26,7 @@
 
 #include "probe.h"
 
-class PolytropeOperator : public mfem::Operator {
+class PolytropeOperator final : public mfem::Operator {
 public:
     PolytropeOperator(
         std::unique_ptr<mfem::MixedBilinearForm> M,
@@ -84,8 +84,8 @@ private:
     /*
      * The schur preconditioner has the form
      *
-     *  ⎡ḟ(θ)^-1  0 ⎤
-     *  ⎣ 0     S^-1 ⎦
+     *  ⎡ḟ(θ)^-1 0 ⎤
+     * ⎣ 0     S^-1 ⎦
      *
      * Where S is the Schur compliment of the system
      *