feat(ffi): add cargo-c support #2900

Job	Run time
Check Style	5s
semver	15s
Verify hyper.h is up to date	18s
features	30s
Test with Miri	2m 18s
Test cargo-c support (FFI)	15s
Test C API (FFI)	17s
minimal-versions	29s
Check MSRV	15s
Test stable on ubuntu-latest	1m 5s
udeps	19s
Test stable on windows-latest	1m 54s
Test stable on macOS-latest	1m 10s
Test beta on ubuntu-latest	1m 7s
Test beta on windows-latest	1m 46s
Test beta on macOS-latest	1m 8s
Test nightly on ubuntu-latest	1m 5s
Test nightly on windows-latest	1m 56s
Test nightly on macOS-latest	1m 29s
Check exposed types	14s
Build docs	13s
CI is green	0s
	18m 8s

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