Read the context window from four more model lists

app/MindWork AI Studio/Provider/Mistral/Model.cs

@@ -1,3 +1,13 @@
+using System.Text.Json.Serialization;
+
 namespace AIStudio.Provider.Mistral;
 
-public readonly record struct Model(string Id, string Object, int Created, string OwnedBy);
+/// <summary>
+/// One model as Mistral lists it.
+/// </summary>
+/// <param name="Id">The model's ID.</param>
+/// <param name="Object">What kind of thing the entry is. Known value: "model".</param>
+/// <param name="Created">When the model was published, as seconds since the epoch.</param>
+/// <param name="OwnedBy">Who Mistral names as the owner of the model.</param>
+/// <param name="ContextWindowTokens">How much the model reads and writes in one conversation, in tokens.</param>
+public readonly record struct Model(string Id, string Object, int Created, string OwnedBy, [property: JsonPropertyName("max_context_length")] int? ContextWindowTokens);