Read the context window from four more model lists

app/MindWork AI Studio/Provider/Groq/GroqModel.cs

@@ -0,0 +1,15 @@
+using System.Text.Json.Serialization;
+
+namespace AIStudio.Provider.Groq;
+
+/// <summary>
+/// One model as Groq lists it.
+/// </summary>
+/// <remarks>
+/// Groq says more about a model than the shared OpenAI-compatible list does, which is why this
+/// provider brings a data model of its own instead of using that one: the shared record is read by
+/// a dozen providers, and a field only one of them sends has no business in it.
+/// </remarks>
+/// <param name="Id">The model's ID.</param>
+/// <param name="ContextWindowTokens">How much the model reads and writes in one conversation, in tokens.</param>
+public readonly record struct GroqModel(string Id, [property: JsonPropertyName("context_window")] int? ContextWindowTokens);