Use tiktoken instead of GPT2Tokenizer

[laipz8200]

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1. Is this request related to a challenge you're experiencing? Tell me about your story.

Because it's faster.

2. Additional context or comments

No response

3. Can you help us with this feature?

• I am interested in contributing to this feature.

[yihong0618]

that will be good and GPT2Tokenizer cost almost 50MB memory