PoC of introducing `FromSpoofableRequestParts` and `Spoofable` #4976

Job	Run time
check	1m 32s
cargo-public-api-crates (axum)	34s
cargo-hack	4m 45s
cargo-deny check (advisories)	23s
cargo-public-api-crates (axum-core)	20s
check-docs	29s
cargo-public-api-crates (axum-extra)	32s
cargo-deny check (bans licenses sources)	26s
cargo-public-api-crates (axum-macros)	17s
dependencies-are-sorted	16s
Spell Check with Typos	5s
test-nightly	1m 33s
test-docs	1m 32s
test-versions (stable)	2m 40s
test-msrv	2m 35s
test-versions (beta)	2m 22s
armv5te-unknown-linux-musleabi	46s
wasm32-unknown-unknown	22s
	21m 29s

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