Closes https://github.com/zed-industries/zed/issues/63314 Closes https://github.com/zed-industries/zed/issues/42584 Follow-up to https://github.com/zed-industries/zed/pull/62652 Removes a lot of duplicated code in favor of throwing it into`language_core` as well as removing duplicate struct definitions that were only different because of entirely unused fields. Furthermore, improves error-messages so that these untagged enum errors are no longer a thing in an effort to make this more maintainable in the future. Lastly, includes a small but nice improvement changing a `Value` to a `RawValue` so that we don't have to clone for deserialization in that specific case. Release Notes: - Improved streaming for OpenAI-compatible providers. --------- Co-authored-by: Anant Goel <anant@zed.dev>