PoV Distribution optimization (#1990)

* Initial commit

* Remove unnecessary struct

* Some review nits

* Update node/network/pov-distribution/src/lib.rs

* Update parachain/test-parachains/adder/collator/tests/integration.rs

* Review nits

* notify_all_we_are_awaiting

* Both ways of peers connections should work the same

* Add mod-level docs to error.rs

* Avoid multiple connection requests at same parent

* Dont bail on errors

* FusedStream for ConnectionRequests

* Fix build after merge

* Improve error handling

* Remove whitespace formatting