Refactor in support of future OAS 3.1 work #1225

Job	Run time
rustfmt	20s
test (stable)	32s
test (beta)	2m 19s
test (nightly)	2m 18s
test (nightly-musl)	2m 31s
test (nightly-mips)	3m 13s
test (nightly-32)	1m 40s
test (macos)	1m 4s
test (win-msvc)	1m 51s
test (win-gnu)	2m 8s
test (msrv)	5m 39s
test (wasm32, ubuntu-latest, nightly)	1m 9s
	24m 44s

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