Fixes#752
Fix the issue with loading the tokenizer for 'gpt2'.
* **scrapegraphai/utils/tokenizer.py**
- Add a check for `GPT2TokenizerFast` in the `num_tokens_calculus` function.
- Import `GPT2TokenizerFast` from `transformers`.
* **scrapegraphai/utils/tokenizers/tokenizer_ollama.py**
- Modify the `num_tokens_ollama` function to handle `GPT2TokenizerFast`.
* **tests/graphs/smart_scraper_ollama_test.py**
- Add a test case to verify the tokenizer loading for `GPT2TokenizerFast`.
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