Add differential testing harness #260

Job	Run time
Test (windows-2022, x86_64-pc-windows-msvc)	49s
Test (ubuntu-20.04, x86_64-unknown-linux-gnu)	44s
Lint	55s
cargo-deny	52s
Test (ubuntu-20.04, aarch64-linux-android, x86_64-unknown-linux-gnu)	45s
Test (macOS-latest, x86_64-apple-darwin)	45s
test_success	0s
	4m 50s

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