test: `arbitrary` feature separation #88

Job	Run time
Clippy	14s
Miri (x86_64-unknown-linux-gnu)	28s
feature checks	13s
Miri (aarch64-unknown-linux-gnu)	31s
Test (aarch64-unknown-linux-gnu, nightly)	32s
docs	16s
Test (aarch64-unknown-linux-gnu, stable)	30s
fmt	11s
Outdated	0s
Test (aarch64-unknown-linux-gnu, 1.64)	9m 44s
Test (i686-unknown-linux-gnu, nightly)	32s
Test (i686-unknown-linux-gnu, stable)	28s
Test (i686-unknown-linux-gnu, 1.64)	9m 31s
Test (x86_64-unknown-linux-gnu, nightly)	14s
Test (x86_64-unknown-linux-gnu, stable)	9s
Test (x86_64-unknown-linux-gnu, 1.64)	9m 16s
	32m 49s

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