Fix: Ensure EntityConverter delegates to AIEntityConverter

[msftshlomiyosef]

Fixes #298
Ensure EntityConverter checks if the value is an AIEntity and delegates serialization, so @type, @context, and @id are included.

[Copilot]

Pull Request Overview

This PR updates the JSON serialization behavior to honor JsonIgnore and JsonPropertyName attributes by adding caching for reflection lookups and updating the property mapping logic. Key changes include:

• Introducing GetCachedProperties and GetPropertyMap in ConnectorConverter to improve performance and respect JSON attributes.
• Updating tests to validate derived types, proper handling of ignored properties, and thread safety.
• Enabling JsonPropertyName attributes on AIEntity properties and removing redundant manual property handling in AIEntityConverter.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/tests/Microsoft.Agents.Model.Tests/ObjectSerializationTests.cs	Added tests for derived entity serialization, thread safety, and validation using new attributes.
src/libraries/Core/Microsoft.Agents.Core/Serialization/Converters/ConnectorConverter.cs	Introduced property caching and mapping to respect JsonIgnore and JsonPropertyName.
src/libraries/Core/Microsoft.Agents.Core/Serialization/Converters/AIEntityConverter.cs	Removed manual extension data handling to rely on attribute-based mapping via the base.
src/libraries/Core/Microsoft.Agents.Core/Models/AIEntity.cs	Uncommented and activated JsonPropertyName attributes for correct JSON property naming.

[tracyboehrer]

Does #305 replace this PR?

[msftshlomiyosef]

Does #305 replace this PR?

@tracyboehrer
This PR solves a very specific problem of serializing AIEntity when the compile-time type is Entity, while preserving the approach of manually handling custom property names in the converters.
#305 solves a broader problem but changes this approach, so it can replace this PR if we agree to adopt the new model.

[tracyboehrer]

@msftshlomiyosef I'm all for this route if it works. Entities in general were made to be subclassed, so obeying the attributes is of benefit.

[msftshlomiyosef]

Closing this, as it will be handled here: #305