feat(engine): Optional Serde #3935

Job	Run time
doctest	1m 45s
test ubuntu-latest stable --no-default-features	45s
check no_std	28s
test ubuntu-latest stable	1m 34s
clippy	58s
test ubuntu-latest stable --all-features	2m 16s
docs	1m 13s
test ubuntu-latest nightly --no-default-features	1m 4s
feature-checks	1m 42s
test ubuntu-latest nightly	1m 25s
wasm-unknown	55s
test ubuntu-latest nightly --all-features	2m 2s
wasm-wasi	1m 44s
test ubuntu-latest 1.79 --no-default-features	47s
cfg-check	32s
test ubuntu-latest 1.79	46s
fmt	14s
test windows-latest stable --no-default-features	4m 24s
test windows-latest stable	4m 15s
test windows-latest stable --all-features	5m 4s
test windows-latest nightly --no-default-features	3m 15s
test windows-latest nightly	4m 10s
test windows-latest nightly --all-features	4m 49s
test windows-latest 1.79 --no-default-features	3m 45s
test windows-latest 1.79	3m 37s
	53m 29s

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