fix: align PNL0003 Reynolds diagnostic with AMESim

app/simulation/core/medium.py

@@ -81,6 +81,8 @@ class GasMedium(Protocol):
 
     def dynamic_viscosity(self, T: float) -> float: ...
 
+    def diagnostic_dynamic_viscosity(self, T: float) -> float: ...
+
     def specific_internal_energy(self, T: float) -> float: ...
 
     def specific_internal_energy_at_pressure(self, p: float, T: float) -> float: ...
@@ -182,6 +184,16 @@ class IdealGasMedium:
             / (T + self.sutherland_constant)
         )
 
+    def diagnostic_dynamic_viscosity(self, T: float) -> float:
+        """Return the viscosity convention used by derived diagnostics.
+
+        Most media use the same transport property for dynamics and reported
+        diagnostics. Reference-library media may override this without
+        changing a calibrated constitutive flow relation.
+        """
+
+        return self.dynamic_viscosity(T)
+
     @profile_property("specific_internal_energy")
     def specific_internal_energy(self, T: float) -> float:
         delta_T = T - self.T_ref