Add codes for LLM4Chem dataset

[coldchair]

Add support for the LLM4Chem dataset and its subtasks

This PR adds dataset integration for LLM4Chem(https://github.com/OSU-NLP-Group/LLM4Chem) with support for the following subtasks:

'forward_synthesis',
'retrosynthesis',
'molecule_captioning',
'molecule_generation',
'name_conversion-i2f',
'name_conversion-i2s',
'name_conversion-s2f',
'name_conversion-s2i',
'property_prediction-esol',
'property_prediction-lipo',
'property_prediction-bbbp',
'property_prediction-clintox',
'property_prediction-hiv',
'property_prediction-sider',
'retrosynthesis_uspto50k'

Notes:

• retrosynthesis_uspto50k comes from otori-bird/retrosynthesis(https://github.com/otori-bird/retrosynthesis) and has been integrated seamlessly with the other retrosynthesis tasks.
• The content within <think></think> will be removed.
• Some metrics currently support only top-1; top-k support is yet to be developed (mainly depending on framework support).