fix: harden electronics shop io parsing

[Cintu07]

PR Description

This pull request hardens the HackerRank Electronics Shop solution by addressing several runtime error sources and improving input handling.

Changes Made

• Added robust input validation
  • Used getline checks to prevent segmentation faults from empty/malformed input.
  • Updated split_string to safely handle empty strings and malformed input.
• Improved output logic
  • Implemented automatic fallback to cout if OUTPUT_PATH is unset.
  • Guarded file opening to prevent crashes outside HackerRank.
• Streamlined file/stream handling
  • Ensured all writes use a consistent output stream.
  • Files are only closed when they were opened, ensuring clean exit paths.

Verification Steps

• Compiled and tested with:

  g++ -std=c++17 Electronics_Shop.cpp -o /tmp/electronics_shop
  

• Verified against:
  • Empty and malformed input scenarios
  • Multiple edge cases (no crash, correct output)
  • Running in environments without OUTPUT_PATH

References

• Fixes Issue #6845: Potential Runtime Errors in Budget Shopping Calculator