fix: add default special tokens

tokenizer_config.json

@@ -5,5 +5,8 @@
       "tokenization_arcade100k.Arcade100kTokenizer",
       null
     ]
-  }
+  },
+  "bos_token": "<|endoftext|>",
+  "eos_token": "<|endoftext|>",
+  "pad_token": "<|endoftext|>"
 }