feat(ffi): add cargo-c support #2901

Job	Run time
Check Style	7s
semver	31s
Verify hyper.h is up to date	12s
features	36s
Test cargo-c support (FFI)	28s
Test C API (FFI)	23s
Check MSRV	16s
Test with Miri	2m 30s
Test stable on ubuntu-latest	1m 14s
udeps	23s
Test stable on windows-latest	2m 36s
minimal-versions	25s
Test stable on macOS-latest	1m 1s
Test beta on ubuntu-latest	1m 13s
Test beta on windows-latest	2m 5s
Test beta on macOS-latest	1m 13s
Test nightly on ubuntu-latest	1m 5s
Test nightly on windows-latest	1m 54s
Test nightly on macOS-latest	1m 31s
Check exposed types	14s
Build docs	18s
CI is green	0s
	20m 15s

Provide feedback