Fix issue #2842: Handle qpdf exit code 3 as success with warnings

[Abdurrahman-shaikh]

Description of Changes

Please provide a summary of the changes, including:

• What was changed:

  • Modified the ProcessExecutor class to accept exit code 3 from qpdf as a success with warnings.
  • Added a check to ensure that only qpdf’s exit code 3 is treated as a warning.
  • Added a warning log for qpdf exit code 3 to provide better visibility into the repair process.

• Why the change was made:

  • The repair process was failing when qpdf returned exit code 3, even though the operation succeeded with warnings. This caused unnecessary errors for users.
  • The changes ensure that PDFs with minor structural issues (e.g., mismatched object counts) are still repaired successfully, while logging warnings for transparency.
  • Added a check to ensure that only qpdf’s exit code 3 is treated as a warning, preventing potential issues with other tools that might use exit code 3 for actual errors.

Closes #2842

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Checklist

General

• I have read the Contribution Guidelines
• I have read the Stirling-PDF Developer Guide (if applicable)
• I have performed a self-review of my own code
• My changes generate no new warnings

Testing (if applicable)

• I have tested my changes locally.
  • Verified that exit code 3 is only treated as a warning for qpdf and not for other tools.

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Additional Notes

• The changes align with qpdf's behavior, where exit code 3 indicates a successful operation with warnings.
• Added a check to ensure that only qpdf’s exit code 3 is treated as a warning, preventing potential issues with other tools.

[Abdurrahman-shaikh]

Looking forward to feedback on this! Let me know if any improvements or refinements are required