Create option pricing engine structure, test architecture.

tests/stubs/FlatYieldCurve.hpp

@@ -0,0 +1,16 @@
+//
+// Created by David Doebel  on 07.03.2026.
+//
+#ifndef QUANTENGINE_FLATYIELDCURVE_HPP
+#define QUANTENGINE_FLATYIELDCURVE_HPP
+#include "YieldCurve.hpp"
+#include <cmath>
+
+class FlatYieldCurve : public YieldCurve{
+
+    double discount(double t) override {return std::exp(-rate_ * t); };
+    double zeroRate(double t) override {return rate_; }
+private:
+    double rate_ = 0.01;
+};
+#endif