Adapt client to support asynchronous backing #2445

Job	Run time
set-tags	4s
check-copyright	3s
cargo-clippy	2m 9s
cargo-toml-feature-propagation	1m 51s
toml-formatting	57s
build	5m 37s
typescript-formatting	17s
typescript-linting	16s
check-api-augment	1m 0s
rust-test	3m 42s
typescript-dancebox-specs	29s
docker-tanssi (tanssi)	42s
chopsticks-upgrade-test (stagenet_dancebox, dancebox)	39s
docker-tanssi (container-chain-simple-template)	39s
chopsticks-upgrade-test (flashbox, flashbox)	37s
docker-tanssi (container-chain-evm-template)	38s
chopsticks-upgrade-test (dancebox, dancebox)	55s
chopsticks-upgrade-test (frontier_template, container-chain-template-frontier)	40s
typescript-tests	6m 26s
typescript-tests-flashbox	3m 2s
typescript-tests-frontier	4m 33s
zombienet-tests-rotation	7m 50s
zombienet-tests	11m 19s
typescript-tests-simple-template	2m 11s
zombienet-tests-warp-sync	6m 55s
zombienet-test-upgrade (dancebox)	3m 45s
	1h 7m 16s

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