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/Option.cpp

@@ -0,0 +1,11 @@
+/**
+ * @file Option.cpp
+ * @brief @ref Option implementation.
+ */
+
+#include "Option.hpp"
+
+Option::Option(double maturity, std::unique_ptr<Exercise> exercise, std::unique_ptr<Payoff> payoff,
+    std::unique_ptr<PricingEngine> engine) : Instrument(maturity, std::move(payoff),
+        std::move(engine)), exercise_(std::move(exercise)){
+}