Macro hygiene: `chain!` and qualified paths #935

Job	Run time
check format	7s
doc	8s
check	23s
check (--no-default-features)	28s
msrv	1m 14s
semver-checks	2m 25s
test	1m 5s
check (--no-default-features --features use_alloc)	11s
check (--all-targets --all-features)	27s
All checks succeeded	1s
	6m 29s

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