Function parse_compression_backend_name_method 

pub fn parse_compression_backend_name_method(
    name: &str,
    method: Option<&str>,
    rate_backend: Option<RateBackend>,
    options: &CompressionBackendShorthandOptions,
) -> SpecResult<CompressionBackend>

Build a compression backend from shorthand CLI/Python-style name + optional method inputs.