Fixed adding Enum and integer

[StefH]

No description provided.

[Copilot]

Pull Request Overview

This PR fixes the handling of arithmetic operations between Enum types and integers in the dynamic LINQ parser. Previously, enums were treated as Int64 for type compatibility checks, which caused incorrect behavior when adding enums and integers.

Key Changes:

• Changed enum type compatibility from TypeCode.Int64 to TypeCode.Int32 to match C#'s actual enum underlying type behavior
• Updated decimal conversion logic to properly handle nullable enum types
• Added comprehensive test coverage for enum arithmetic operations

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/System.Linq.Dynamic.Core/Parser/TypeHelper.cs	Updated IsCompatibleWith to use Int32 for enums instead of Int64, renamed variables for clarity, and added TypesAreEqual helper method
src/System.Linq.Dynamic.Core/Parser/ExpressionPromoter.cs	Fixed decimal conversion check to handle nullable types correctly using new TypesAreEqual method
test/System.Linq.Dynamic.Core.Tests/Parser/TypeHelperTests.cs	Added comprehensive test coverage for enum type compatibility and renamed existing tests for clarity
test/System.Linq.Dynamic.Core.Tests/QueryableTests.Select.cs	Added integration tests for enum+integer and integer+enum addition operations

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