Make axum generic over it's Listener type #4419

Job	Run time
check-docs	31s
check	43s
cargo-hack	1m 12s
cargo-public-api-crates (axum)	31s
cargo-public-api-crates (axum-core)	23s
cargo-deny check (advisories)	27s
cargo-public-api-crates (axum-extra)	32s
dependencies-are-sorted	14s
Spell Check with Typos	6s
cargo-deny check (bans licenses sources)	23s
cargo-public-api-crates (axum-macros)	15s
test-docs	1m 52s
test-nightly	32s
test-msrv	2m 43s
armv5te-unknown-linux-musleabi	45s
test-versions (stable)	2m 40s
wasm32-unknown-unknown	21s
test-versions (beta)	1m 15s
	15m 25s

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