refactor(behaviors): use ZMK_BEHAVIOR_OPAQUE and ZMK_BEHAVIOR_TRANSPARENT

Use these instead of the magic return values 0 and 1 for
behavior_driver_api return values.

app/include/zmk/behavior.h

@@ -6,6 +6,9 @@
 
 #pragma once
 
+#define ZMK_BEHAVIOR_OPAQUE 0
+#define ZMK_BEHAVIOR_TRANSPARENT 1
+
 struct zmk_behavior_binding {
     char *behavior_dev;
     uint32_t param1;