- Add `tokio` dev-dependency so examples can run.
- Create `examples/calorie.rs` that streams a vision request: it sends an image URL plus a prompt asking for calorie estimation and prints the response.
- Extend `TypedChatMessageContent` with convenience constructors `text_content` and `image_url_content`.
- Change `ChatMessageContentValue::TypedContent` to `TypedContentList`, now holding a vector, and update `Display` to concatenate all parts.
- Add `ChatMessage::user_text_message` helper for quick text-only user messages.

- Wraps the single image_url content block in an array to match the new
  TypedContentList format
- Adjusts the assertion to compare against a vec![...] instead of a lone
  TypedChatMessageContent

- Introduced `chat_completion()` that returns a single `ChatMessage` instead of a stream.
- Removed streaming logic from `examples/calorie.rs` and switched to the new method.
- Dropped unused `futures_util` imports from the example.

Rewrote non streaming response parser to use mutable `Value` manipulation (`remove`, `as_array_mut`, `as_object_mut`) instead of chained immutable accessors, avoiding unnecessary clones.

Nit change:
- Replaced commented-out `///` doc line with proper `//!` crate-level doc.
- Removed unused `use reqwest;` import in error module.
- Simplified `Error::cause` implementation by replacing `and_then` with `map`.
- Adopted field-init shorthand (`base_url`, `auth_token`) in `ChatClient::init`.