Get rid of `Peerset` compatibility layer (#14337)

* Move bootnodes from individual `SetConfig`s to `PeersetConfig`

* Move `SetId` & `SetConfig` from `peerset` to `protocol_controller`

* Remove unused `DropReason`

* Move `Message` & `IncomingIndex` from `peerset` to `protocol_controller`

* Restore running fuzz test

* Get rid of `Peerset` in `fuzz` test

* Spawn runners instead of manual polling in `fuzz` test

* Migrate `Protocol` from `Peerset` to `PeerStore` & `ProtocolController`

* Migrate `NetworkService` from `Peerset` to `PeerStore` & `ProtocolController`

* Migrate `Notifications` from `Peerset` to `ProtocolController`s

* Migrate `Notifications` tests from `Peerset` to `ProtocolController`

* Fix compilation of `NetworkService` & `Protocol`

* Fix borrowing issues in `Notifications`

* Migrate `RequestResponse`from `Peerset` to `PeerStore`

* rustfmt

* Migrate request-response tests from `Peerset` to `PeerStore`

* Migrate `reconnect_after_disconnect` test to `PeerStore` & `ProtocolController`

* Fix `Notifications` tests

* Remove `Peerset` completely

* Fix bug with counting sync peers in `Protocol`

* Eliminate indirect calls to `PeerStore` via `Protocol`

* Eliminate indirect calls to `ProtocolController` via `Protocol`

* Handle `Err` outcome from `remove_peers_from_reserved_set`

* Add note about disconnecting sync peers in `Protocol`

* minor: remove unneeded `clone()`

* minor: extra comma removed

* minor: use `Stream` API of `from_protocol_controllers` channel

* minor: remove TODO

* minor: replace `.map().flatten()` with `.flat_map()`

* minor: update `ProtocolController` docs

* rustfmt

* Apply suggestions from code review

Co-authored-by: Aaro Altonen <[email protected]>

* Extract `MockPeerStore` to `mock.rs`

* Move `PeerStore` initialization to `build_network`

* minor: remove unused import

* minor: clarify error message

* Convert `syncs_header_only_forks` test into single-threaded

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Co-authored-by: Aaro Altonen <[email protected]>