Implement static polymorphism using CRTP pattern

[konard]

Summary

Implements static polymorphism in the C++ version using the Curiously Recurring Template Pattern (CRTP) as requested in issue #79.

• Added missing Polymorph.h - Provides CRTP base class implementation
• Enables compile-time polymorphism - Methods resolve statically without virtual function overhead
• Preserves existing API - All current code using this->object() works unchanged
• Comprehensive testing - Added test cases demonstrating functionality

Implementation Details

The Polymorph<TSelf> class provides:

• object() method returning reference to derived class (TSelf&)
• const object() method for read-only access
• constexpr and noexcept qualifiers for optimal performance
• Full compatibility with existing template hierarchy

Pattern Usage

template <typename TSelf, typename TElement>
class Base : public Polymorph<TSelf>
{
    void method() { 
        this->object().derivedMethod(); // Static dispatch
    }
};

class Derived : public Base<Derived, int>
{
    void derivedMethod() { /* implementation */ }
};

Test Plan

✅ Basic CRTP functionality - Verified static dispatch works correctly
✅ Collections pattern - Tested with simulated DoublyLinkedList methods
✅ Compilation - Ensures no build errors with new header
✅ Performance - All method calls resolve at compile time

🤖 Generated with Claude Code

---

Resolves #79