Added support for Perplexity (#545)

Co-authored-by: Thorsten Sommer <mail@tsommer.org>

app/MindWork AI Studio/Provider/ContentStreamChunk.cs

@@ -0,0 +1,16 @@
+namespace AIStudio.Provider;
+
+/// <summary>
+/// A chunk of content from a content stream, along with its associated sources.
+/// </summary>
+/// <param name="Content">The text content of the chunk.</param>
+/// <param name="Sources">The list of sources associated with the chunk.</param>
+public sealed record ContentStreamChunk(string Content, IList<ISource> Sources)
+{
+    /// <summary>
+    /// Implicit conversion to string.
+    /// </summary>
+    /// <param name="chunk">The content stream chunk.</param>
+    /// <returns>The text content of the chunk.</returns>
+    public static implicit operator string(ContentStreamChunk chunk) => chunk.Content;
+}