Add MITC4 drilling diagnostics output and comparison contract

tests/reference/eigen_reference_comparison.h

@@ -7,6 +7,7 @@
 #include <vector>
 
 #include "fesa/core/status.h"
+#include "mitc4_drilling_report.h"
 #include "reference_tolerance_policy.h"
 
 namespace fesa::test {
@@ -36,6 +37,7 @@ struct EigenReferenceComparisonReport {
   bool passed;
   std::string policy_id;
   double relative_rms_tolerance;
+  std::optional<Mitc4DrillingDiagnosticsReport> drilling_diagnostics;
 };
 
 /// @brief Compares modal eigenvalues without changing the approved input or