Feedback on Rust client generator

Feedback from @dctaf on the Rust client generator:

• Rust: The feature set matrix for the Rust clients is misleading:
  It does support bearer-style "Authorizations" but the table suggests otherwise.
  There are "X" marks in allOf and anyOf but this is incorrect or at least misleading.

• Rust: When supportMultipleResponses=true, the generated Success and Failure types are awkward to use. Generating code similar to this would make API use much more ergonomic:

 impl CreateExperimentSuccess {
   fn into_status200(self) -> Result<CreateExperimentResponse> {
     match self {
       Self::Status200(resp) => Ok(resp),
       Self::UnknownValue(_) => anyhow::bail!("unexpected response variant"),
     }
   }
}

• Rust: The documentation would benefit from examples of how the calling interfaces differ when library={hyper,reqwest,reqwest-trait}.

If anyone wants to work on these improvements, please reply to let us know.

Start with the Rust client generator areas responsible for the feature set matrix, multiple-response types, and library-specific documentation. Compare the matrix with the stated bearer, allOf, and anyOf support, review the supportMultipleResponses output and the hyper, reqwest, and reqwest-trait interfaces. Done means the reported inaccuracies are corrected, response use is more ergonomic, and the documentation includes the requested examples.