Using `tractor.trionics.collapse_eg()` as needed and doing
some renames, in similar style as elsewhere:
- `pcs` -> `rent_cs`,
- `n` -> `tn` for nursery handles,
Also,
- tweak the `._reconnect_forever()` while loop to use the
(also) `trio`-internal
`mc_state: trio._channel.MemoryChannelState = snd._state` instead
of `snd._close` to poll for open send/receive consumer task counts
since,
1. it seems more reliable then using the `snd._closed`,
2. there's no other way to access the info.. afaik?
- handle `ConnectionRejected` explicitly alongside handshake-errs as
a retry case.
- add a base-exc handler which `.exception()` reports the reconnect
attempt failure explicitly.
- drop some lingering `Optional` usage.
d35e1e5c67