Internalize IChatClient implementations and auto-configure RawRepresentationFactory

[Copilot]

Makes all IChatClient implementations internal (providers are the public API now) and eliminates the need for explicit ApplyExtensions() calls by auto-configuring RawRepresentationFactory when OpenAI-specific extension properties are set.

Changes

• Internal chat clients: OpenAIChatClient, AzureOpenAIChatClient, AzureInferenceChatClient are now internal
• Auto-configured factory: Setting ReasoningEffort or Verbosity automatically installs the RawRepresentationFactory
• Moved extension properties: ReasoningEffort and Verbosity moved from ChatExtensions to OpenAIExtensions namespace with documentation clarifying OpenAI Responses API specificity
• Validation: Throws InvalidOperationException if RawRepresentationFactory is already set to a custom factory
• Removed ExtendedChatOptions: Replaced with OpenAIChatOptions in the OpenAI namespace for config binding
• Removed ApplyExtensions(): No longer needed

Before

var options = new ChatOptions { ReasoningEffort = ReasoningEffort.High };
await chat.GetResponseAsync(messages, options.ApplyExtensions());

After

var options = new ChatOptions { ReasoningEffort = ReasoningEffort.High };
await chat.GetResponseAsync(messages, options); // Factory auto-configured on property set

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

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

• kzu.blob.core.windows.net
  • Triggering command: /usr/bin/dotnet dotnet restore (dns block)
  • Triggering command: /usr/bin/dotnet dotnet restore --no-dependencies /home/REDACTED/work/Extensions.AI/Extensions.AI/src/Extensions.CodeAnalysis/Extensions.CodeAnalysis.csproj --packages /home/REDACTED/work/Extensions.AI/.codeql-scratch/dbs/csharp/working/packages /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal /p:TargetFrameworkRootPath=/home/REDACTED/work/Extensions.AI/.codeql-scratch/dbs/csharp/working/emptyFakeDotnetRoot /p:NetCoreTargetingPackRoot=/home/REDACTED/work/Extensions.AI/.codeql-scratch/dbs/csharp/working/emptyFakeDotnetRoot (dns block)

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

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Original prompt

I'd like all IChatClient implementations to be purely internal (since we have the providers now).
As part of this change, I'd like the ApplyExtensions for OpenAI-extended properties via ChatOptions to be unnecessary in the following way:

• on set of any of the extension properties, we'd set the RawRepresentationFactory to point to a method on a singleton factory static factory/method to apply the properties as needed.
• The extension properties would be OpenAI-specific rather than generic. They would contain documentation highlighting that they are to be used only with the Responses API.
• If the representation factory is set to some other factory, we'll throw.
• ExtendedChatOptions should be gone since it's not used at all

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[kzu]

🧪 Details on Ubuntu 24.04.3 LTS

from retest v1.1.0 on .NET 10.0.2 with 💜 by @devlooped