Support 449 `Retry With` Status Code

Could a 449 status code be added to `StatusCode`? It is a Microsoft Specific code, so that may make it out of scope, especially if adhering to [this list](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status). If so, could an `Other(u16)` option be added or is the objective to force failed conversion if not explicitly defined? https://http.dev/449

Start by locating the StatusCode definition and the conversion behavior referenced in the issue. Check how unsupported HTTP codes are handled, then confirm whether 449 should be explicitly supported or represented through a fallback; done means the chosen behavior is covered by the existing project checks.

Written by the indexing model from the issue text.