CSV file path handling in substrait.py example

[Ritinikhil]

• Add cross-platform path handling using os.path
• Add error handling for CSV file registration

[SanjayUG]

Hi there,

I am interested in handling this bug

Could you please assign me for the contribution.

Thank You.

[timsaucer]

Closing since examples seem to be working. Please reopen with specific method to reproduce the error if this continues to be an issue.