Feature request: Add Exit Codes for Comparison and Report Generation

[Oleksiichchch]

Hi,

Thank you for your work on testcafe-blink-diff! It's a great tool, and I've found it very useful.

However, I'm currently facing a challenge when integrating this tool into CI/CD pipeline. Specifically, there are no distinct exit codes for comparison results and report generation outcomes. Without these, I'm forced to implement a workaround by parsing the HTML report, which feels like a hack.

To improve the usability of testcafe-blink-diff in automated environments, I propose adding standard exit codes, like:

0 - Success: No visual differences found, and report generation successful.
1 - Visual Differences Found: The comparison detected visual differences.
2 - Report Generation Error: The comparison completed, but there was an error generating the report.
3 - Comparison Error: An error occurred during the comparison process.