feat(core): 添加 command 定义及 command_buffer 维护功能

src/core/runtime.h

@@ -3,6 +3,7 @@
 #include <stddef.h>
 
 #include "core/backend.h"
+#include "core/command_buffer.h"
 #include "core/layout.h"
 #include "core/rules.h"
 #include "core/state.h"
@@ -23,6 +24,7 @@ typedef struct runtime_t {
   bool running;
   bool will_restart;
 
+  command_buffer_t command_buffer;
   state_t state;
   layout_registry_t layouts;
   rules_t rules;