[Feature]: Add edge case tests for Statistics Engine

[rahuldass19]

Which engine does this affect?

Stats Verifier

Is this feature deterministic?

Yes - Pure symbolic/math/logic

Problem Statement

Currently, the Statistics Engine lacks test coverage for edge cases like:

• Empty data arrays
• Single element arrays
• Very large numbers (overflow)
• Negative numbers in variance calculations

This makes it harder for first-time contributors to understand expected behavior.

Proposed Solution

Add comprehensive edge case tests to tests/test_stats_verifier.py.

This is beginner-friendly work - estimated ~1-2 hours.

Alternatives Considered

N/A - Tests are the standard approach for edge case coverage.

Checklist

• I have read CONTRIBUTING.md
• This is NOT an enterprise feature (audit, SSO, RBAC)