Make mruby raii cleanup, and fix cleanup bug.

- Functions were cleaned up after mruby, which was wrong.
- Becuase functions could have stored a reference to a Block which refers to mruby.
- And so it would crash on release builds at exit if custom functions were used.

include/internal/scripting/ruby.h

@@ -4,6 +4,30 @@
 #include "pch.h"
 
 namespace bed::internal::scripting {
+struct RubyState {
+  mrb_state *state = nullptr;
+  int arena = 0;
+
+  explicit RubyState(BEd *ctx) : state(mrb_open()) {
+    if (!state)
+      throw fatal_error("Failed to initialize mruby.", 1);
+    state->ud = ctx;
+    arena = mrb_gc_arena_save(state);
+  }
+
+  ~RubyState() {
+    state->ud = nullptr;
+    if (state) {
+      mrb_gc_arena_restore(state, arena);
+      mrb_full_gc(state);
+      mrb_close(state);
+    }
+  }
+
+  RubyState(const RubyState &) = delete;
+  RubyState &operator=(const RubyState &) = delete;
+};
+
 struct Block {
   mrb_state *mrb = nullptr;
   mrb_value proc = mrb_nil_value();