Jack Wrenn 0d41b373e7 core, subscriber: more downcast_ref & is methods (#2160)
Adds inherent `downcast_ref` and `is` inherent methods to:
  - `dyn Subscriber + Send`
  - `dyn Subscriber + Sync`
  - `dyn Subscriber + Send + Sync`
  - `Layered`

These additional implementations reduce the circumstances in which one
must cast to `dyn Subscriber` (which, previously, was the only type for
which `downcast_ref` and `is` were available).
2022-06-22 15:01:24 -07:00
..
2022-04-19 18:11:09 +00:00