[rust] set useAsyncFileStream only for files in the body #667

Job	Run time
Build Rust (samples/client/petstore/rust/)	1m 15s
Build Rust (samples/server/petstore/rust-server-deprecated/)	4m 22s
Build Rust (samples/client/others/rust/)	1m 26s
Build Rust (samples/server/petstore/rust-server/)	3m 39s
Build Rust (samples/server/petstore/rust-axum/)	2m 47s
	13m 29s

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