Rust

Add `Point::serialized_len` #364

Job	Run time
check-alloc	6s
check	48s
check-all	39s
check-nostd	11s
fmt	13s
test	25s
build-wasm	55s
build-wasm-nostd	24s
check-changelog	2s
check-doc	45s
check-semver (generic-ec, all-features)	28s
clippy-nostd	54s
clippy	11s
clippy-tests	15s
check-semver (generic-ec, only-explicit-features)	3m 2s
check-semver (generic-ec-core, all-features)	57s
check-semver (generic-ec-core, only-explicit-features)	2m 21s
check-semver (generic-ec-curves, all-features)	33s
check-semver (generic-ec-curves, only-explicit-features)	2m 29s
check-semver (generic-ec-zkp, all-features)	19s
check-semver (generic-ec-zkp, only-explicit-features)	2m 33s
	18m 30s

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