PoC of introducing `FromSpoofableRequestParts` and `Spoofable` #4975

Job	Run time
cargo-hack	5m 3s
check-docs	28s
cargo-public-api-crates (axum)	34s
check	1m 30s
dependencies-are-sorted	13s
cargo-public-api-crates (axum-core)	22s
cargo-deny check (advisories)	26s
Spell Check with Typos	9s
cargo-public-api-crates (axum-extra)	26s
cargo-deny check (bans licenses sources)	23s
cargo-public-api-crates (axum-macros)	22s
test-docs	0s
test-nightly	0s
armv5te-unknown-linux-musleabi	0s
test-msrv	0s
test-versions	0s
wasm32-unknown-unknown	0s
	9m 56s

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