There was a problem with visibility state from proc that straddles a fiber or is independent.
Therefore, it has been changed to give priority to env objects, if any.
Also, added "separate module" flag to block traversal to a higher level env object.
Note that the "separate module" flag is now set when calling blocks with the `mrb_yield_with_class()` function.
fixed https://github.com/mruby/mruby/issues/6494
dearblue
3fd5e1c250