Update String Transform Examples

[lamarrr]

Description

This pull request makes changes needed for the string transforms examples. It:

• Fixes an overflow in calculating the scratch space
• Updates the CSV row per chunk to speed up csv write
• Adds missing NVTX range to cudf::io::write_csv
• Renames the source files for the examples

Closes #19041

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[GregoryKimball]

@mhaseeb123 Is this where you would put the scoped range?

[mhaseeb123]

Seems ok to me as this is the main CSV write function that gets called from cudf::io::write_csv and I don't see any CUDF_FUNC_RANGE() in any of the functions called from in here so this one should capture the complete write_csv time. In future, we might want to put scoped ranges in maybe (write_chunked_begin and write_chunked for better granularity). Wdyt @vuule ?

[ttnghia]

Typically, scoped range is used to make a range within a code block. That means, we can have multiple scoped ranges in a single function. On the other hand, CUDF_FUNC_RANGE is used to generate a (scoped)range for the entire function, at the top function level.

[ttnghia]

I see that this scoped range is at the top function level so it should be equivalent to CUDF_FUNC_RANGE.