[Python][Docs] Add code examples for compute function first/last/first_last

[zhengruifeng]

Describe the enhancement requested

Add code examples for compute function first/last/first_last

Component(s)

Python, Documentation

[vanshaj2023]

Hi! I'd like to work on this issue.

Implementation approach:

1. Locate the compute function documentation for first, last, and first_last in the Python docs
2. Add practical code examples demonstrating:
   • Basic usage with arrays
   • Using the skip_nulls parameter (if applicable)
   • Different input types (arrays, chunked arrays)
   • Expected output for each function
3. Follow the existing documentation style/format used for other compute functions

Could you please assign this issue to me? Also, let me know if this approach looks good or if I'm missing something.

Thanks!

[AlenkaF]

Issue resolved by pull request 49270
#49270