Improve physical geometry, fluid solvers, audio, and profiling

include/FluidSim/TwoStrokeCylinder.hpp

@@ -23,6 +23,9 @@ public:
     void set_crankcase(Crankcase& crankcase) { crankcase_ = &crankcase; }
     void set_carburetor(Carburetor& carburetor) { carburetor_ = &carburetor; }
     float transfer_width{.050f}, exhaust_width{.036f};
+    // Retained as two-stroke compatibility metadata; port areas come from the
+    // transfer and exhaust geometry above rather than poppet valve motion.
+    float intake_valve_lift{}, exhaust_valve_lift{};
     float minimum_burn_seconds{.0008f};
     std::uint64_t combustion_count() const { return combustion_count_; }