feat(furvm): add collect function to context

furvm/src/context.cpp

@@ -1,7 +1,16 @@
 #include "furvm/context.hpp"
 
+#include "furvm/thing.hpp" // IWYU pragma: keep
+
 namespace furvm {
 
 context::context() {}
 
+void context::collect() {
+    for (auto& ref : m_things) {
+        if (ref->reference_count() != 0) continue;
+        ref = nullptr;
+    }
+}
+
 } // namespace furvm

furvm/src/main.cpp

@@ -25,8 +25,12 @@ int main(void) {
     auto executor = furvm::executor::create(context);
     executor->push_frame(mainModule, 0);
 
+    static constexpr std::size_t FPC = 3; // Frames per collection
+
+    std::size_t count = 0;
     while ((executor->flags() & furvm::executor_flags::Done) != furvm::executor_flags::Done) {
         executor->step();
+        if ((++count % FPC) == 0) context->collect();
     }
 
     return 0;