Tests

Add the modifies_memory macro #3091

Job	Run time
check serde	19s
check no-default-features	19s
check std	25s
clippy	1m 23s
docs	1m 8s
fmt	5s
test stable --no-default-features	1m 8s
test no_std	20s
test stable	51s
test stable --all-features	1m 16s
test beta --no-default-features	54s
test beta	54s
test beta --all-features	1m 24s
test nightly --no-default-features	53s
test nightly	57s
test nightly --all-features	1m 29s
	13m 45s

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