Make unbounded channels size warning exact (part 1) (#13490)

* Replace `futures-channel` with `async-channel` in `out_events`

* Apply suggestions from code review

Co-authored-by: Koute <koute@users.noreply.github.com>

* Also print the backtrace of `send()` call

* Switch from `backtrace` crate to `std::backtrace`

* Remove outdated `backtrace` dependency

* Remove `backtrace` from `Cargo.lock`

---------

Co-authored-by: Koute <koute@users.noreply.github.com>

substrate/Cargo.lock

@@ -326,6 +326,17 @@ version = "1.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9b34d609dfbaf33d6889b2b7106d3ca345eacad44200913df5ba02bfd31d2ba9"
 
+[[package]]
+name = "async-channel"
+version = "1.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf46fee83e5ccffc220104713af3292ff9bc7c64c7de289f66dae8e38d826833"
+dependencies = [
+ "concurrent-queue",
+ "event-listener",
+ "futures-core",
+]
+
 [[package]]
 name = "async-io"
 version = "1.12.0"
@@ -8626,9 +8637,9 @@ version = "0.10.0-dev"
 dependencies = [
  "array-bytes",
  "assert_matches",
+ "async-channel",
  "async-trait",
  "asynchronous-codec",
- "backtrace",
  "bytes",
  "either",
  "fnv",