Fix mapping of MinLength/MaxLength/Length attribute mapping in nullable string properties.

[eiriktsarpalis]

Fix #6676

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull Request Overview

This PR fixes a bug in the JSON schema generation where MinLength/MaxLength/Length attributes were incorrectly mapped to minItems/maxItems instead of minLength/maxLength for nullable string properties.

Key Changes:

• Fixed attribute mapping logic to properly handle nullable string types
• Added a helper method to correctly identify string schema types in union types
• Updated test expectations to reflect the correct JSON schema property names

Reviewed Changes

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

File	Description
AIJsonUtilities.Schema.Create.cs	Implements the core fix by adding TryGetSchemaType helper method and updating attribute mapping logic
AIJsonUtilitiesTests.cs	Updates existing test expectations and adds new test case for nullable string properties with length constraints

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[stephentoub]

Thanks