Rust

Fix `serde` module not being available without `serde` feature #256

Job	Run time
test	24s
build	17s
build-alloc	21s
build-wasm	33s
build-wasm-nostd	26s
check-publish (generic-ec)	20s
clippy	19s
check-doc	21s
check-publish (generic-ec-core)	9s
check-publish (generic-ec-curves)	12s
clippy-nostd	26s
check-publish (generic-ec-zkp)	24s
clippy-tests	9s
fmt	9s
build-nostd	12s
check-semver (generic-ec, all-features)	2m 37s
check-semver (generic-ec, only-explicit-features)	2m 29s
check-semver (generic-ec-core, all-features)	2m 24s
check-semver (generic-ec-core, only-explicit-features)	2m 19s
check-semver (generic-ec-curves, all-features)	2m 39s
check-semver (generic-ec-curves, only-explicit-features)	2m 31s
check-semver (generic-ec-zkp, all-features)	2m 37s
check-semver (generic-ec-zkp, only-explicit-features)	2m 27s
	24m 45s

Provide feedback