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/RandomGenerator.hpp

@@ -0,0 +1,31 @@
+/**
+ * @file RandomGenerator.hpp
+ * @brief Random numbers for Monte Carlo (Gaussian draws).
+ */
+
+#ifndef QUANTENGINE_RANDOMGENERATOR_HPP
+#define QUANTENGINE_RANDOMGENERATOR_HPP
+#include <random>
+
+/** @brief Interface for standard normal variates. */
+class RandomGenerator {
+public:
+    RandomGenerator() = default;
+    virtual ~RandomGenerator() = default;
+    virtual double nextGaussian() = 0;
+    virtual std::vector<double> nextGaussianVector(std::size_t n) = 0;
+};
+
+/** @brief @c std::mt19937 with normal distribution. */
+class MersenneTwister : public RandomGenerator {
+public:
+    MersenneTwister() = default;
+    double nextGaussian() override;
+    std::vector<double> nextGaussianVector(std::size_t n) override;
+private:
+    std::mt19937 generator_;
+    std::normal_distribution<> distr_ {0.0, 1.0};
+};
+
+
+#endif //QUANTENGINE_RANDOMGENERATOR_HPP