add Chain of Draft and direct system prompt styles

reasoning_gym/utils.py

@@ -16,6 +16,8 @@
 Do not explain your reasoning inside the answer tags, provide only the final answer. When an example is provided, you should strictly follow the format of the output/answer in that example.
 """,
     "simple": "You are a helpful assistant that answers questions accurately and concisely. When asked to solve a problem, show your work step by step. Provide your final answer between <answer> and </answer> tags.",
+    "direct": "Answer the question directly. Provide your answer between <answer> and </answer> tags. Do not return any preamble, explanation, or reasoning.",
+    "chain_of_draft": "Think step by step, but only keep a minimum draft for each thinking step, with 5 words at most. Return the answer at the end of the response enclosed in <answer> </answer> tags.",
 }