Introduce ZAPDiff CLI

[AryaHassanli]

This PR introduces the zapdiff CLI tool to compare two sets of ZAP XML files and report mismatches in a CSV format.

Changes:

• Added zapdiff package with a pipeline for comparing XML files.
• Implemented element ID generation for ZAP XML elements to identify matching entities across files (essentially an XPath).
• Added mismatch detection for missing tags, missing attributes, and attribute value differences.
• Added CLI command zapdiff to run the comparison and output results to mismatches.csv.
• Implemented sorting of mismatches by Level (Descending), Path, Type, ElementID, and Details for a structured output.

[gemini-code-assist]

Code Review

This pull request adds a zap-diff command to compare ZAP XML files and export inconsistencies to CSV. The review feedback identifies several critical improvements: ensuring unique element IDs to prevent data loss during comparison, implementing recursive file searching to cover the full SDK structure, handling errors during CSV flushing, and optimizing performance through map pre-allocation.