Fix type mapping for equivalent signatures in API comparison

[jbrinkman]

This PR resolves GitHub Issue #40 where type mappings weren't working correctly for generic parameters and equivalent signatures.

Problem

Type mappings like "RedisValue": "ValkeyValue" were configured but still showing as differences in the comparison results. The issue was that equivalent signatures should not appear as differences at all when types are properly mapped.

Root Cause

The issue had two parts:

1. Modified types: Even when types were mapped equivalents, CalculateTypeChanges was comparing raw signatures without considering type mappings
2. Added types: The logic for detecting "added" types was backwards - it tried to map new type names back to old types instead of checking if old types map TO new types

Solution

Key Changes

• Enhanced ApiComparer: Fixed logic to properly check if old types map TO new types for added/removed detection
• Modified DifferenceCalculator: Added optional signaturesEquivalent parameter to CalculateTypeChanges method
• Signature Equivalence: When signatures are equivalent after applying type mappings, no difference is created
• Comprehensive Testing: Added unit tests to validate type mapping scenarios

Interface Changes

• IDifferenceCalculator.CalculateTypeChanges now accepts optional signaturesEquivalent parameter
• Maintains backward compatibility with default value of false

Results

• ✅ Eliminated false positives: Mapped types like RedisValue vs ValkeyValue no longer show as differences
• ✅ Reduced noise: Differences reduced from 902 to 886 (16 fewer false positives)
• ✅ Comprehensive coverage: Type mappings now work correctly for:
  • Basic type equivalence
  • Constructor signatures
  • Generic interface parameters
  • Method parameters and return types
• ✅ All tests passing: 412/412 unit tests pass

Validation

Tested with real-world scenario comparing StackExchange.Redis vs Valkey.Glide assemblies:

• Before: 902 differences (100 added, 791 removed, 11 modified)
• After: 886 differences (95 added, 791 removed, 0 modified)

The mapped types (ValkeyValue, ValkeyKey, ValkeyResult, etc.) no longer appear anywhere in the differences report, confirming the fix works correctly.

Fixes #40