small helpers for alloy serde PR #1689

Job	Run time
docs	55s
feature-checks	4m 25s
clippy	1m 6s
fmt	14s
miri --no-default-features	4m 1s
wasm	40s
miri	4m 4s
miri --all-features	4m 53s
test stable --no-default-features	1m 24s
test stable	1m 24s
test stable --all-features	1m 37s
test beta --no-default-features	51s
test beta	49s
test beta --all-features	1m 18s
test nightly --no-default-features	1m 51s
test nightly	1m 45s
test nightly --all-features	2m 4s
test 1.65 --no-default-features	32s
test 1.65	39s
test 1.65 --features json	37s
	35m 9s

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