Create option pricing engine structure, test architecture.

src/Payoff.cpp

@@ -0,0 +1,18 @@
+//
+// Created by David Doebel  on 05.03.2026.
+//
+
+#include "Payoff.hpp"
+#include <algorithm>
+
+double CallPayoff::operator()(double S) {
+    return std::max(0., S - strike_);
+}
+
+double PutPayoff::operator()(double S) {
+    return std::max(0., strike_ - S);
+}
+
+double DigitalPayoff::operator()(double S) {
+    return S > strike_ ? 1. : 0.;
+}