tb Fix runtime being initialized on every interp_runstring() exec, which causes memory leaks

user/tb/main.c

@@ -4,6 +4,7 @@
 #include "interp.h"
 #include "macros.h"
 #include "config.h"
+#include "runtime.h"
 
 #define LINEBUF_MAX 1024
 
@@ -147,6 +148,7 @@ void main(void) {
   }
 
   set_config();
+  rt_init();
 
   do_file("base:/scripts/rc.tb");