Overseer: subsystems communicate directly (#2227)

* overseer: pass messages directly between subsystems

* test that message is held on to

* Update node/overseer/src/lib.rs

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* give every subsystem an unbounded sender too

* remove metered_channel::name

1. we don't provide good names
2. these names are never used anywhere

* unused mut

* remove unnecessary &mut

* subsystem unbounded_send

* remove unused MaybeTimer

We have channel size metrics that serve the same purpose better now and the implementation of message timing was pretty ugly.

* remove comment

* split up senders and receivers

* update metrics

* fix tests

* fix test subsystem context

* fix flaky test

* fix docs

* doc

* use select_biased to favor signals

* Update node/subsystem/src/lib.rs

Co-authored-by: Andronik Ordian <write@reusable.software>

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>
Co-authored-by: Andronik Ordian <write@reusable.software>

polkadot/Cargo.lock

@@ -4236,12 +4236,6 @@ dependencies = [
  "parking_lot 0.11.1",
 ]
 
-[[package]]
-name = "oorandom"
-version = "11.1.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0ab1bc2a289d34bd04a330323ac98a1b4bc82c9d9fcb1e66b63caa84da26b575"
-
 [[package]]
 name = "opaque-debug"
 version = "0.2.3"
@@ -5886,12 +5880,12 @@ dependencies = [
 name = "polkadot-overseer"
 version = "0.1.0"
 dependencies = [
+ "assert_matches",
  "async-trait",
  "femme",
  "futures 0.3.13",
  "futures-timer 3.0.2",
  "kv-log-macro",
- "oorandom",
  "polkadot-node-network-protocol",
  "polkadot-node-primitives",
  "polkadot-node-subsystem",