Implement `FromRequestParts` for `Parts` and `Extensions` #4034

Job	Run time
check	46s
cargo-hack	3m 14s
check-docs	26s
cargo-public-api-crates (axum)	31s
cargo-public-api-crates (axum-core)	22s
cargo-deny check (advisories)	27s
dependencies-are-sorted	13s
Spell Check with Typos	5s
cargo-public-api-crates (axum-extra)	28s
cargo-deny check (bans licenses sources)	26s
cargo-public-api-crates (axum-macros)	14s
test-versions (stable)	1m 48s
test-docs	1m 42s
test-versions (beta)	2m 0s
armv5te-unknown-linux-musleabi	33s
test-msrv	1m 24s
wasm32-unknown-unknown	24s
test-nightly	1m 33s
	16m 36s

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