feat(ffi): add cargo-c support #2902

Job	Run time
Verify hyper.h is up to date	24s
semver	11s
Check Style	5s
Check MSRV	15s
Test stable on ubuntu-latest	1m 3s
Test stable on windows-latest	2m 17s
Test C API (FFI)	14s
features	31s
Test stable on macOS-latest	1m 24s
Test cargo-c support (FFI)	38s
Test beta on ubuntu-latest	1m 7s
minimal-versions	25s
Test beta on windows-latest	1m 59s
Test with Miri	2m 16s
udeps	23s
Test beta on macOS-latest	1m 4s
Test nightly on ubuntu-latest	1m 4s
Test nightly on windows-latest	2m 0s
Test nightly on macOS-latest	1m 28s
Build docs	14s
Check exposed types	15s
CI is green	0s
	19m 17s

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