Remove duplicate oneOf schemas during pre-processing #591

Job	Run time
Build Rust (samples/client/petstore/rust/)	1m 3s
Build Rust (samples/server/petstore/rust-axum/)	56s
Build Rust (samples/server/petstore/rust-server/)	2m 9s
Build Rust (samples/client/others/rust/)	31s
	4m 39s

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