add eval and potentially speed up variable access speeds when multi threading. fix bug in threading count

src/built-ins.go

@@ -19,6 +19,7 @@ func makeGlobal() ArObject {
 		"client": builtinFunc{"client", ArSocketClient},
 	})
 	vars["infinity"] = infinity
+	vars["eval"] = builtinFunc{"eval", AReval}
 	vars["map"] = builtinFunc{"map", func(a ...any) (any, ArErr) {
 		if len(a) == 0 {
 			return Map(anymap{}), ArErr{}