Tests

feat: add `abigen!` macro #919

Job	Run time
no-std build	2m 37s
Unix tests (ubuntu-latest, stable)	15m 57s
Windows tests (stable, x86_64-pc-windows-gnu)	14m 37s
WASM tests	7m 44s
Windows tests (stable, x86_64-pc-windows-msvc)	20m 2s
Unix tests (ubuntu-latest, nightly)	16m 4s
Windows tests (nightly, x86_64-pc-windows-gnu)	9m 39s
Unix tests (macos-11, stable)	15m 59s
Unix tests (macos-11, nightly)	15m 58s
Windows tests (nightly, x86_64-pc-windows-msvc)	20m 12s
	2h 18m 49s

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