Tests

feat: add `abigen!` macro #907

Job	Run time
no-std build	2m 39s
Unix tests (ubuntu-latest, stable)	3m 29s
Unix tests (ubuntu-latest, nightly)	3m 28s
WASM tests	12m 14s
Unix tests (macos-11, stable)	4m 18s
Windows tests (stable, x86_64-pc-windows-gnu)	10m 53s
Unix tests (macos-11, nightly)	17m 11s
Windows tests (stable, x86_64-pc-windows-msvc)	8m 35s
Windows tests (nightly, x86_64-pc-windows-gnu)	8m 47s
Windows tests (nightly, x86_64-pc-windows-msvc)	9m 47s
	1h 21m 21s

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