fix: add input validation for CSV import (#554)

[AyeshaaRafaqat]

Fixes #554

• Validates CRE column format matches XXX-XXX| pattern
• Returns descriptive 400 error instead of generic 500
• Handles triple-quoted text edge case

Tested locally by reproducing both cases from the issue.

[AyeshaaRafaqat]

@northdpole would appreciate any feedback on the approach here happy to make changes based on your review.

[PRAteek-singHWY]

Hi @AyeshaaRafaqat , thanks for working on this!

Just a heads up , this issue is also being addressed in PR #682 and PR #683 , which is currently under maintainer review. I hadn’t linked it to the issue earlier while working on it, because it was part of while I was working on MyOpenCRE milestone and was suggested by @northdpole to move my logic into "spreadsheet_parsers.py" with a new function
" def validate_import_csv_rows "

U can refer to this for more information -> #584 (comment)

Flagging this here so maintainers are aware of the overlap and can decide the best path forward. Appreciate the effort on this!
Great work!