Add New FieldCalculationMap FieldMap Using NCalc for Integer Computation

[Copilot]

This PR implements a new FieldCalculationMap that enables mathematical calculations on numeric fields during Azure DevOps work item migrations using NCalc expressions.

Changes Made

Core Implementation

• Added FieldCalculationMapOptions in MigrationTools project with:

  • expression: NCalc-compatible formula (e.g., "[x]*2")
  • parameters: Dictionary mapping variable names to source field reference names
  • targetField: Destination field reference name
  • ApplyTo: Optional list of work item types (inherited from base class)

• Added FieldCalculationMap in MigrationTools.Clients.TfsObjectModel project with:

  • Safe NCalc expression evaluation with error handling
  • Field existence validation for both source and target fields
  • Support for numeric field types (int, long, double, decimal)
  • Automatic type conversion for target field compatibility
  • Comprehensive logging for debugging and error reporting

Dependencies

• Added ncalc v1.3.8 package to Directory.Packages.props
• Referenced ncalc in MigrationTools.Clients.TfsObjectModel project

Testing

• Created comprehensive unit tests (FieldCalculationMapTests) covering:
  • Configuration validation and setup
  • NCalc expression evaluation (simple, complex, division, math functions)
  • Error handling for invalid expressions and undefined variables
  • All 8 new tests pass successfully

Usage Example

{
  "FieldMapType": "FieldCalculationMap",
  "ApplyTo": ["Bug", "Task"],
  "expression": "[effort] * [rate]",
  "parameters": {
    "effort": "Custom.EstimatedHours",
    "rate": "Custom.HourlyRate"
  },
  "targetField": "Custom.EstimatedCost"
}

Technical Details

• Safe Evaluation: Uses NCalc's synchronous evaluation to prevent security issues
• Field Validation: Validates all referenced fields exist before attempting calculations
• Type Safety: Converts numeric types appropriately for target field compatibility
• Error Resilience: Gracefully handles missing fields, invalid expressions, and type conversion errors with detailed logging
• Architecture Compliance: Follows existing FieldMap patterns and naming conventions

Testing Results

• ✅ All projects build successfully
• ✅ All existing tests continue to pass (25 tests)
• ✅ New unit tests validate core functionality (8 tests)
• ✅ No breaking changes to existing functionality

Fixes #2745.

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