Codegen revamp #797

Job	Run time
verify-codegen-crate	1m 55s
format	12s
clippy (async-std-surf)	1m 34s
test (async-std-surf)	4m 6s
clippy (tokio-hyper)	1m 13s
test (tokio-hyper)	4m 51s
Docs	49s
clippy (tokio-hyper-rustls)	1m 10s
test (tokio-hyper-rustls)	4m 43s
clippy (tokio-hyper-rustls-webpki)	1m 10s
test (tokio-hyper-rustls-webpki)	4m 43s
clippy (blocking)	1m 19s
test (blocking)	4m 58s
clippy (blocking-rustls)	1m 5s
test (blocking-rustls)	5m 3s
clippy (blocking-rustls-webpki)	1m 2s
test (blocking-rustls-webpki)	5m 17s
	45m 10s

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