feat!: add function calling support to client.chat() & client.chat_async()

BREAKING CHANGE: Too many to count in this version. Check the README examples.

examples/list_models.rs

@@ -0,0 +1,10 @@
+use mistralai_client::v1::client::Client;
+
+fn main() {
+    // This example suppose you have set the `MISTRAL_API_KEY` environment variable.
+    let client = Client::new(None, None, None, None).unwrap();
+
+    let result = client.list_models().unwrap();
+    println!("First Model ID: {:?}", result.data[0].id);
+    // => "First Model ID: open-mistral-7b"
+}