Migrate MEF calculator from VB.NET to C#

[devin-ai-integration]

Summary

Migrate the MEF (Managed Extensibility Framework) calculator from VB.NET to C# while preserving identical functionality and architecture. This creates a complete C# version of the three-project solution alongside the existing VB.NET version.

Link to Devin run: https://app.devin.ai/sessions/0e94d4220b8d4e02b086a640022be689
Requested by: @ankehao-dev

Changes Made

• SimpleCalculator2: Main console application with MEF composition logic
• MefCalculator: Shared interfaces library (ICalculator, IOperation, IOperationData) with basic Add/Subtract operations
• ExtendedOperations: Extension library with Modulo operation that dynamically loads into Extensions directory
• Target Framework: Updated to .NET 8.0 for all projects (from .NET 7.0/.NET Standard 2.0) for testing compatibility

Key Architecture Preserved

• MEF composition with AggregateCatalog combining multiple sources
• Dynamic loading from Extensions subdirectory
• Same project structure and dependencies as VB.NET version
• Interactive console loop with identical parsing and error handling

Testing Performed

Verified functionality with basic operations:

• Addition: 5+3 → 8 ✓
• Subtraction: 10-4 → 6 ✓
• Modulo (extension): 8%3 → 2 ✓
• Error handling: invalid input → "Could not parse command." ✓
• Extensions loading confirmation message ✓

Review Checklist

Critical items to verify:

1. MEF Composition Logic - Verify the AggregateCatalog setup, AssemblyCatalog references, and DirectoryCatalog for Extensions loading match VB.NET behavior
2. Project Output Paths - Confirm ExtendedOperations correctly outputs to ../bin/Debug/Extensions/ for dynamic MEF loading
3. C# Syntax Conversion - Compare string parsing logic, null handling, and exception patterns against VB.NET original
4. Target Framework - Evaluate if .NET 8.0 upgrade is appropriate vs keeping original .NET 7.0/.NET Standard 2.0
5. Error Message Consistency - Verify error handling produces identical output to VB.NET version

Medium priority:

• Project references and Private/CopyLocal settings match VB.NET
• Namespace usage and imports are correct
• Console interaction loop behavior is identical

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