feat: add chat completion without streaming

src/v1/error.rs

@@ -0,0 +1,15 @@
+use std::error::Error;
+use std::fmt;
+
+#[derive(Debug)]
+pub struct APIError {
+    pub message: String,
+}
+
+impl fmt::Display for APIError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "APIError: {}", self.message)
+    }
+}
+
+impl Error for APIError {}