Better handling of metadata in allOf #615

Job	Run time
Build Rust (samples/server/petstore/rust-axum/)	1m 6s
Build Rust (samples/server/petstore/rust-server/)	2m 22s
Build Rust (samples/client/petstore/rust/)	1m 2s
Build Rust (samples/client/others/rust/)	41s
	5m 11s

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