Add EnumType attribute to enum fields when they are generated as string so they can be linked back to their source enum type

[matnun-br]

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[Copilot]

Pull Request Overview

This PR adds an EnumTypeAttribute to enum fields when they are generated as strings, enabling them to be linked back to their source enum type. This provides metadata that can be used to maintain the connection between string-represented enum values and their original enum definitions.

• Introduces a new EnumTypeAttribute class to store enum type metadata
• Modifies the field generation logic to apply this attribute to enum fields when using string representation

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 2 comments.

File	Description
GraphQLSharp/Abstractions/EnumTypeAttribute.cs	Defines the new attribute class for storing enum type information
GraphQLSharp/TypeGenerator/GraphQLTypeGenerator.cs	Updates field generation to conditionally apply the EnumType attribute to enum fields

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