This change is adding commentary about the upcoming API removal and
simplification of nursery + portal internals; no actual code changes are
included.
The plan to (re)move the old RPC methods:
- `ActorNursery.run_in_actor()`
- `Portal.run()`
- `Portal.run_from_ns()`
and any related impl internals out of each conc-primitive and instead
into something like a `.hilevel.rpc` set of APIs which then are all
implemented using the newer and more lowlevel `Context`/`MsgStream`
primitives instead Bo
Further,
- formally deprecate the `Portal.result()` meth for
`.wait_for_result()`.
- only `log.info()` about runtime shutdown in the implicit root case.
2ac999cc3c