Fix incorrect-equality false positives for boundary constants

[ep0chzer0]

Summary

• Comparisons against boundary values (0, type(T).max) should not be flagged as dangerous strict equalities
• These values cannot be manipulated by an attacker to break the equality check

Root Cause

The detector flags all strict equality comparisons involving tainted values (balances, timestamps, etc.) without considering whether the comparison target is a safe boundary value.

Fix

Added is_comparing_against_safe_constant() method that excludes:

• Literal 0 - cannot reach zero by adding value
• type(T).max values - cannot reach max through normal operations

Test Coverage

Updated test file with new cases:

• good4/good5() - comparing block.timestamp/number == 0 (NOT flagged)
• TestSafeConstants.good0/1/2() - comparing balance against 0 and type(uint256).max (NOT flagged)
• bad0/bad1() - comparing against arbitrary values 1, 100 (STILL flagged)

Impact

• Eliminates false positives for common patterns like balance == 0 and allowance == type(uint256).max
• Maintains detection of genuinely dangerous comparisons like balance == 100 ether

Fixes #2759