Added support for Perplexity (#545)

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

app/MindWork AI Studio/Provider/Perplexity/ResponseStreamLine.cs

@@ -0,0 +1,45 @@
+namespace AIStudio.Provider.Perplexity;
+
+/// <summary>
+/// Data model for a line in the response stream, for streaming completions.
+/// </summary>
+/// <param name="Id">The id of the response.</param>
+/// <param name="Object">The object describing the response.</param>
+/// <param name="Created">The timestamp of the response.</param>
+/// <param name="Model">The model used for the response.</param>
+/// <param name="SystemFingerprint">The system fingerprint; together with the seed, this allows you to reproduce the response.</param>
+/// <param name="Choices">The choices made by the AI.</param>
+public readonly record struct ResponseStreamLine(string Id, string Object, uint Created, string Model, string SystemFingerprint, IList<Choice> Choices, IList<SearchResult> SearchResults) : IResponseStreamLine
+{
+    /// <inheritdoc />
+    public bool ContainsContent() => this != default && this.Choices.Count > 0;
+
+    /// <inheritdoc />
+    public ContentStreamChunk GetContent() => new(this.Choices[0].Delta.Content, this.GetSources());
+    
+    /// <inheritdoc />
+    public bool ContainsSources() => this != default && this.SearchResults.Count > 0;
+
+    /// <inheritdoc />
+    public IList<ISource> GetSources() => this.SearchResults.Cast<ISource>().ToList();
+}
+
+/// <summary>
+/// Data model for a choice made by the AI.
+/// </summary>
+/// <param name="Index">The index of the choice.</param>
+/// <param name="Delta">The delta text of the choice.</param>
+public readonly record struct Choice(int Index, Delta Delta);
+
+/// <summary>
+/// The delta text of a choice.
+/// </summary>
+/// <param name="Content">The content of the delta text.</param>
+public readonly record struct Delta(string Content);
+
+/// <summary>
+/// Data model for a search result.
+/// </summary>
+/// <param name="Title">The title of the search result.</param>
+/// <param name="URL">The URL of the search result.</param>
+public sealed record SearchResult(string Title, string URL) : Source(Title, URL);