Restructure C++ core into cpp module and package bindings.

Move the pricing engine sources out of src/ into cpp/, add the closed-form engine and pybind wiring, and align tests/build targets with the new project layout.

Made-with: Cursor

cpp/Statistics.hpp

@@ -0,0 +1,33 @@
+/**
+ * @file Statistics.hpp
+ * @brief Online sample moments for Monte Carlo diagnostics.
+ */
+
+#ifndef QUANTENGINE_STATISTICS_HPP
+#define QUANTENGINE_STATISTICS_HPP
+#include <vector>
+
+/**
+ * @brief Accumulates count, mean/variance-related sums, and running min/max.
+ */
+class Statistics {
+public:
+    Statistics() : moments_({0., 0., 0.}), n(0), max_(0.), min_(0.) {}
+    void dump(double value);
+    void clear();
+    double mean();
+    double variance();
+    double standardDeviation();
+    double skewness();
+    double max();
+    double min();
+    double sum();
+    double count();
+private:
+    std::vector<double> moments_;
+    std::size_t n;
+    double max_, min_;
+};
+
+
+#endif //QUANTENGINE_STATISTICS_HPP