Add 'developer' to Role type in types.ts (#56)

Author: rileytomasek

src/types.ts

@@ -1,7 +1,13 @@
 import { type OpenAI } from '../openai-types/index.js';
 
 /** The possible roles for a message. */
-export type Role = 'system' | 'user' | 'assistant' | 'function' | 'tool';
+export type Role =
+  | 'system'
+  | 'developer'
+  | 'user'
+  | 'assistant'
+  | 'function'
+  | 'tool';
 
 /** The name and arguments of a function that should be called, as generated by the model. */
 export type FunctionCall = {