[Fusion] Remove Debug.Assert around MoveNext() calls

[tobias-tengler]

Debug.Assert calls are removed in Release builds, so the enumerator was never advanced in those cases leading to an exception for operations querying affected fields.

Also fixes that __typename on any introspection type like __Schema always returned Query.

[Copilot]

Pull Request Overview

This PR fixes a critical bug where Debug.Assert calls were being used to advance enumerators in release builds, causing enumerators to never advance and resulting in exceptions for operations querying affected fields.

• Replaces Debug.Assert calls with direct MoveNext() calls in introspection code
• Fixes TypeNameField to correctly reference the selection set's type instead of the root operation type
• Adds a new test case to verify __typename functionality on introspection types

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
TypeNameField.cs	Fixed to use correct type reference for __typename field resolution
__Type.cs	Replaced Debug.Assert with direct MoveNext() calls for enumerator advancement
__Directive.cs	Replaced Debug.Assert with direct MoveNext() call for enumerator advancement
IntrospectionTests.cs	Added test case and refactored existing test structure
IntrospectionTests.Typename_On_Introspection_Types.yaml	Test snapshot for new introspection functionality

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

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