refactor(furvm): expose context thing allocator

Refs: #12

furvm/include/furvm/context.hpp

@@ -92,6 +92,8 @@ public:
     auto erase_thing(Args&&... args) {
         return m_things.erase(std::forward<Args>(args)...);
     }
+
+    thing_allocator<std::byte> thing_alloc() const { return m_thingAllocator; }
 public:
     /**
      * @brief Removes unreferenced things from the thing list.

furvm/src/executor.cpp

@@ -78,7 +78,7 @@ void executor::step() {
     switch (instr) {
     case instruction_t::NoOperation: break;
     case instruction_t::PushB2I: {
-        push_thing({ thing_t::Int32, m_context->m_thingAllocator })->int32() = frame.mod->byte(frame.position++);
+        push_thing({ thing_t::Int32, m_context->thing_alloc() })->int32() = frame.mod->byte(frame.position++);
     } break;
     case instruction_t::Drop: {
         pop_thing();