mruby.h: simplify task state definitions using fiber state aliases

remove MRB_TASK_CREATED and MRB_TASK_STOPPED from mrb_fiber_state enum
and define them as aliases to MRB_FIBER_CREATED and MRB_FIBER_TERMINATED.

this makes the relationship between tasks and fibers clearer and avoids
artificially extending the enum with semantically equivalent values.

Co-authored-by: Claude <noreply@anthropic.com>

include/mruby.h

@@ -187,12 +187,12 @@ enum mrb_fiber_state {
   MRB_FIBER_SUSPENDED,
   MRB_FIBER_TRANSFERRED,
   MRB_FIBER_TERMINATED,
-#ifdef MRB_USE_TASK_SCHEDULER
-  MRB_TASK_CREATED,
-  MRB_TASK_STOPPED,
-#endif
 };
 
+/* Task context status aliases */
+#define MRB_TASK_CREATED MRB_FIBER_CREATED
+#define MRB_TASK_STOPPED MRB_FIBER_TERMINATED
+
 struct mrb_context {
   struct mrb_context *prev;