Add analyzer "Lookup Must Not Return List Type"

[glen-84]

Summary of the changes (Less than 80 chars)

• Add analyzer "Lookup Must Not Return List Type".

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#8072

[Copilot]

Pull request overview

Adds a new Roslyn analyzer to enforce that members annotated with [Lookup] do not return list-like types, aligning with Hot Chocolate best practices and the analyzer roadmap in issue #8072.

Changes:

• Introduce analyzer HC0114: “Lookup Must Not Return List Type” (error) for methods/properties decorated with [Lookup].
• Update the existing Lookup must return nullable type analyzer to avoid double-reporting when the return type is a list.
• Add analyzer tests + snapshot baselines covering list/array/IEnumerable and Task<List<T>> return types.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/HotChocolate/Core/src/Types.Analyzers/LookupReturnsListTypeAnalyzer.cs	New analyzer that reports HC0114 when [Lookup] returns array or supported list-like types.
src/HotChocolate/Core/src/Types.Analyzers/LookupReturnsNonNullableTypeAnalyzer.cs	Skips list/array return types to avoid overlapping diagnostics with the new analyzer.
src/HotChocolate/Core/src/Types.Analyzers/Errors.cs	Adds the HC0114 diagnostic descriptor.
src/HotChocolate/Core/test/Types.Analyzers.Tests/TestHelper.cs	Registers the new analyzer in the test analyzer set.
src/HotChocolate/Core/test/Types.Analyzers.Tests/LookupReturnsListTypeAnalyzerTests.cs	New unit tests validating HC0114 triggers and non-trigger scenarios.
src/HotChocolate/Core/test/Types.Analyzers.Tests/snapshots/*.md	Snapshot outputs verifying generated sources and analyzer diagnostics for the new rule.

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