In a previous PR ([Rust ]Add async file stream support for reqwest client): the useAsyncFileStream and vendorExtensions.useAsyncFileStream template variables are used in case there's at least one file uploaded in the body, but they are set as long as supportAsync is set and any parameter is a file (including if the file is in a form). So these variables are set more often than they should, introducing unused dependencies on tokio.

This explains why on master, these tests have the tokio dependency even though they don't use it:

• samples/client/petstore/rust/reqwest/petstore-async-tokensource/Cargo.toml
• samples/client/petstore/rust/reqwest/petstore-async-middleware/Cargo.toml
• samples/client/petstore/rust/reqwest/petstore-async/Cargo.toml
• samples/client/petstore/rust/reqwest/petstore-avoid-box/Cargo.toml

This PR sets the useAsyncFileStream and vendorExtensions.useAsyncFileStream template variables only when at least one body parameter is a file.

This PR doesn't break the feature introduced by [Rust ]Add async file stream support for reqwest client, as can be seen in the samples/client/others/rust/reqwest/file-streaming example.

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