Add delta to mds converter

[XiaohanZhangCMU]

Description of changes:

• Introduced a utility function for converting a Spark DataFrame into an MDS format.
• This utility function is flexible and supports a callable function, allowing modifications to the original data format. The function iterates over the callable, processes the modified data, and writes it in MDS format. For instance, it can be used with a tokenizer callable function that yields tokens as output.
• Included an example Jupyter notebook demonstrating a complete workflow. It illustrates how to transform raw data into a Spark DataFrame and then convert it into the MDS format.

Issue #, if available

STR-111

Merge Checklist:

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[karan6181]

Please clean all the output of jupyter notebook before you add it here.

[Skylion007]

I just realized that while my conversation was marked resolved, nothing actually changed here. The count +=1 is unreachable here now so the error counting is kinda useless.