ci: add a `cargo doc` job #3552

Job	Run time
Audit	24s
Compilation tests	2m 24s
Clippy and fmt	56s
Windows	1m 32s
ubuntu-latest 1.80.0	8m 4s
ubuntu-latest 1.80.0 --features unstable,legacy,__abi-generate	17m 25s
ubuntu-latest stable	7m 31s
ubuntu-latest stable --features unstable,legacy,__abi-generate	15m 37s
macos-latest 1.80.0	3m 45s
macos-latest 1.80.0 --features unstable,legacy,__abi-generate	9m 16s
macos-latest stable	4m 0s
macos-latest stable --features unstable,legacy,__abi-generate	7m 28s
cargo-doc	1m 16s
	1h 19m 38s

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