modity code structure

Former-commit-id: 0682ed357210897e0b67c4a6eb31a94b3eb929f1

src/llmtuner/tuner/__init__.py

@@ -0,0 +1,5 @@
+from llmtuner.tuner.core import get_train_args, get_infer_args, load_model_and_tokenizer
+from llmtuner.tuner.pt import run_pt
+from llmtuner.tuner.sft import run_sft
+from llmtuner.tuner.rm import run_rm
+from llmtuner.tuner.ppo import run_ppo