feat(engine): Optional Serde #3941

Job	Run time
test ubuntu-latest stable --no-default-features	1m 11s
test ubuntu-latest stable	1m 18s
wasm-unknown	43s
wasm-wasi	1m 22s
test ubuntu-latest stable --all-features	2m 17s
doctest	1m 10s
test ubuntu-latest nightly --no-default-features	1m 5s
test ubuntu-latest nightly	1m 15s
cfg-check	28s
check no_std	24s
test ubuntu-latest nightly --all-features	1m 53s
test ubuntu-latest 1.79 --no-default-features	31s
clippy	32s
docs	59s
test ubuntu-latest 1.79	41s
test windows-latest stable --no-default-features	5m 12s
feature-checks	3m 22s
fmt	11s
test windows-latest stable	4m 37s
test windows-latest stable --all-features	5m 27s
test windows-latest nightly --no-default-features	3m 12s
test windows-latest nightly	4m 9s
test windows-latest nightly --all-features	4m 4s
test windows-latest 1.79 --no-default-features	3m 7s
test windows-latest 1.79	3m 4s
	52m 14s

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