Stream the tool calling rounds of every Chat Completions provider

app/MindWork AI Studio/Provider/OpenAI/ChatCompletionToolStreamChoice.cs

@@ -0,0 +1,9 @@
+namespace AIStudio.Provider.OpenAI;
+
+/// <summary>
+/// One choice of a streamed Chat Completions answer, as the tool calling rounds read it.
+/// </summary>
+/// <param name="Index">The index of the choice; we only ever work with the first one.</param>
+/// <param name="Delta">What this line adds to the choice.</param>
+/// <param name="FinishReason">Why the model stopped, set on the last line of the choice.</param>
+public sealed record ChatCompletionToolStreamChoice(int Index, ChatCompletionStreamDelta? Delta, string? FinishReason);