Improve test coverage of the Notifications protocol (#13033)

* Add handler and upgrade tests

* Add tests for `behaviour.rs`

* Apply review comments

* Update dependencies

* Apply suggestions from code review

Co-authored-by: Dmitry Markin <dmitry@markin.tech>

* Apply review comments

* Fix clippy

* Update mockall

* Apply review comment

---------

Co-authored-by: Dmitry Markin <dmitry@markin.tech>

substrate/client/network/Cargo.toml

@@ -28,6 +28,7 @@ ip_network = "0.4.1"
 libp2p = { version = "0.50.0", features = ["dns", "identify", "kad", "macros", "mdns", "mplex", "noise", "ping", "tcp",  "tokio", "yamux", "websocket"] }
 log = "0.4.17"
 lru = "0.8.1"
+mockall = "0.11.3"
 parking_lot = "0.12.1"
 pin-project = "1.0.12"
 rand = "0.8.5"
@@ -52,9 +53,12 @@ sp-runtime = { version = "7.0.0", path = "../../primitives/runtime" }
 
 [dev-dependencies]
 assert_matches = "1.3"
+multistream-select = "0.12.1"
+rand = "0.8.5"
 tempfile = "3.1.0"
 tokio = { version = "1.22.0", features = ["macros"] }
 tokio-util = { version = "0.7.4", features = ["compat"] }
+tokio-test = "0.4.2"
 sc-network-light = { version = "0.10.0-dev", path = "./light" }
 sc-network-sync = { version = "0.10.0-dev", path = "./sync" }
 sp-test-primitives = { version = "2.0.0", path = "../../primitives/test-primitives" }