chore: feature gate serde #5877

Job	Run time
feature-checks	4m 36s
doctest	2m 0s
test ubuntu-latest stable --no-default-features	1m 38s
wasm-unknown	1m 12s
test ubuntu-latest stable	1m 48s
wasm-wasi	2m 5s
check no_std	24s
test ubuntu-latest stable --all-features	2m 30s
clippy	1m 6s
test ubuntu-latest nightly --no-default-features	1m 24s
feature-propagation	50s
docs	1m 0s
test ubuntu-latest nightly	1m 19s
fmt	12s
test ubuntu-latest nightly --all-features	2m 4s
test ubuntu-latest 1.81 --no-default-features	59s
test ubuntu-latest 1.81	1m 12s
test windows-latest stable --no-default-features	6m 5s
test windows-latest stable	4m 25s
test windows-latest stable --all-features	8m 50s
test windows-latest nightly --no-default-features	3m 37s
test windows-latest nightly	3m 15s
test windows-latest nightly --all-features	5m 37s
test windows-latest 1.81 --no-default-features	3m 10s
test windows-latest 1.81	3m 13s
deny / cargo deny check	22s
ci success	2s
	1h 4m 55s

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