Reduce dependency on `futures-util` #5505

Job	Run time
cargo-hack	6m 10s
check	47s
check-docs	37s
cargo-public-api-crates (axum)	54s
cargo-deny check (advisories)	23s
cargo-public-api-crates (axum-core)	37s
dependencies-are-sorted	30s
cargo-deny check (bans licenses sources)	24s
Spell Check with Typos	5s
cargo-public-api-crates (axum-extra)	50s
cargo-public-api-crates (axum-macros)	39s
test-docs	0s
test-nightly	0s
armv5te-unknown-linux-musleabi	0s
test-msrv	0s
test-versions	0s
wasm32-unknown-unknown	0s
	11m 56s

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