Allow BYO http impl #874

Job	Run time
assert_full_test_suite	6s
Build x86_64-apple-darwin target	5m 36s
Build aarch64-apple-darwin target	3m 57s
test (ubuntu-latest)	2m 55s
test (macos-latest)	2m 48s
test (windows-latest)	5m 11s
Build x86_64-pc-windows-msvc target	5m 8s
Build x86_64-unknown-linux-gnu target	3m 40s
Build x86_64-unknown-linux-musl target	5m 46s
lint	2m 30s
rust-test	3m 0s
rust-test-vectors	3m 55s
kotlin-build-test-deploy-snapshot	2m 11s
kotlin-acceptance-test (ubuntu-latest)	21s
kotlin-acceptance-test (macos-latest)	21s
kotlin-acceptance-test (macos-12)	22s
kotlin-acceptance-test (windows-latest)	20s
	48m 7s

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