fix(furvm): add stack.hpp

I forgot to add it earlier

furvm/include/furvm/stack.hpp

@@ -0,0 +1,56 @@
+#ifndef FURVM_STACK_HPP
+#define FURVM_STACK_HPP
+
+#include <cstddef>
+#include <new>
+#include <stack>
+
+namespace furvm {
+
+template <typename T>
+struct stack {
+    stack(std::size_t capacity = (1024ULL * 1024ULL) / sizeof(T))
+      : begin(new T[capacity]()), cursor(begin), capacity(capacity) {}
+
+    T*             begin;
+    T*             cursor;
+    std::size_t    capacity;
+    std::stack<T*> frames;
+
+    void push_frame() { frames.push(cursor); }
+
+    void pop_frame() {
+        cursor = frames.top();
+        frames.pop();
+    }
+};
+
+template <typename T>
+class stack_allocator {
+public:
+    stack_allocator() = default;
+
+    stack_allocator(stack<T>& stack)
+      : m_ref(&stack) {}
+
+    template <typename U>
+    constexpr stack_allocator(const stack_allocator<U>& other) noexcept
+      : m_ref(other.m_ref) {}
+public:
+    T* allocate(std::size_t n) {
+        if (m_ref == nullptr) throw std::bad_alloc();
+        if (m_ref->capacity - (m_ref->cursor - m_ref->begin) < n) throw std::bad_alloc();
+
+        T* ptr         = m_ref->cursor;
+        m_ref->cursor += n;
+        return ptr;
+    }
+
+    void deallocate(T* ptr, std::size_t n) {}
+private:
+    stack<T>* m_ref = nullptr;
+};
+
+} // namespace furvm
+
+#endif // FURVM_STACK_HPP