Expose `SerializableMap` #156

Job	Run time
semver	18s
clippy	28s
rustfmt	7s
build-docs	33s
stable-test (x86_64-unknown-linux-gnu, 1.81.0)	41s
test-and-coverage	40s
wasm-build (1.81.0, wasm32-unknown-unknown)	25s
wasm-build (stable, wasm32-unknown-unknown)	17s
	3m 29s

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