if split_special_tokens==True，fast_tokenizer is slower than slow_tokenizer

```python
from transformers import LlamaTokenizer, LlamaTokenizerFast
import time
tokenizer1 = LlamaTokenizer.from_pretrained("./Llama-2-7b-chat-hf", split_special_tokens=True) # LlamaTokenizer
tokenizer2 = LlamaTokenizerFast.from_pretrained("./Llama-2-7b-chat-hf", split_special_tokens=True) # LlamaTokenizer
print(tokenizer1, tokenizer2)

s_time = time.time()
for i in range(1000):
tokenizer1.tokenize("你好，where are you?"*100)
print(f"slow: {time.time() - s_time}")

s_time = time.time()
for i in range(1000):
tokenizer2.tokenize("你好，where are you?"*100)
print(f"fast: {time.time() - s_time}")
```

output:
slow: 0.6021890640258789
fast: 0.7353882789611816