ci: add a `cargo doc` job #3554

Job	Run time
Compilation tests	2m 48s
cargo-doc	1m 45s
Audit	23s
Clippy and fmt	47s
ubuntu-latest 1.80.0	7m 56s
Windows	1m 55s
ubuntu-latest 1.80.0 --features unstable,legacy,__abi-generate	15m 51s
ubuntu-latest stable	7m 41s
ubuntu-latest stable --features unstable,legacy,__abi-generate	15m 26s
macos-latest 1.80.0	4m 57s
macos-latest 1.80.0 --features unstable,legacy,__abi-generate	10m 20s
macos-latest stable	2m 57s
macos-latest stable --features unstable,legacy,__abi-generate	9m 6s
	1h 21m 52s

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