Add headers to client

examples/chat_completion.rs

@@ -6,7 +6,7 @@ use std::env;
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
     let api_key = env::var("OPENAI_API_KEY").unwrap().to_string();
-    let client = OpenAIClient::builder().with_api_key(api_key).build()?;
+    let mut client = OpenAIClient::builder().with_api_key(api_key).build()?;
 
     let req = ChatCompletionRequest::new(
         GPT4_O_MINI.to_string(),
@@ -21,7 +21,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
 
     let result = client.chat_completion(req).await?;
     println!("Content: {:?}", result.choices[0].message.content);
-    println!("Response Headers: {:?}", result.headers);
+    println!("Response Headers: {:?}", client.headers);
 
     Ok(())
 }