Add comprehensive tests for nextLink properties with string types

[Copilot]

This PR addresses the issue where nextLink properties can be strings rather than just URLs by adding comprehensive tests to verify the existing behavior works correctly.

Investigation Summary

During investigation of issue #6778, I discovered that the TypeSpec C# generator already correctly handles nextLink properties that are defined as strings:

• String nextLink: InputPrimitiveType.String → public string NextCat { get; }
• URL nextLink: InputPrimitiveType.Url → public global::System.Uri NextCat { get; }

Changes Made

Added Tests

• NextLinkWithStringType: Verifies that nextLink properties defined as InputPrimitiveType.String generate correct string properties
• NextLinkStringVsUrlComparison: Compares behavior between URL and String nextLink properties side-by-side

Test Results

Both tests demonstrate that the type system correctly:

1. Maps InputPrimitiveType.String to string properties
2. Maps InputPrimitiveType.Url to Uri properties
3. Generates appropriate constructors and serialization code for each type

All existing NextLink tests continue to pass (12/12).

Example Generated Code

String nextLink property:

public string NextCat { get; }

internal PageString(IList<Cat> cats, string nextCat, IDictionary<string, BinaryData> additionalBinaryDataProperties)
{
    Cats = cats;
    NextCat = nextCat; // String assignment
    _additionalBinaryDataProperties = additionalBinaryDataProperties;
}

URL nextLink property:

public global::System.Uri NextCat { get; }

internal PageUrl(IList<Cat> cats, global::System.Uri nextCat, IDictionary<string, BinaryData> additionalBinaryDataProperties)
{
    Cats = cats;
    NextCat = nextCat; // Uri assignment
    _additionalBinaryDataProperties = additionalBinaryDataProperties;
}

Conclusion

The existing codebase already correctly handles the requirement that "nextLink properties can be strings." No code changes to the generator were needed - only additional test coverage to verify and document this capability.

Fixes #6778.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• aka.ms
  • Triggering command: curl -I -sSL --retry 5 --retry-delay 2 --connect-timeout 15 REDACTED (dns block)
• esm.ubuntu.com
  • Triggering command: /usr/lib/apt/methods/https (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list

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