fix file content extractor mechanism ...

Interfaces/Extractors/IXFileContentExtractor.cs

@@ -0,0 +1,26 @@
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace xAiApi.Interfaces.Extractors
+{
+    /// <summary>
+    /// a Service for Extracting File Content ...
+    /// </summary>
+    public interface IXFileContentExtractor
+    {
+        /// <summary>
+        /// Check if this extractor supports the specified MIME type ...
+        /// </summary>
+        bool CanExtract(string mimeType);
+
+        /// <summary>
+        /// Extract text content from file stream ...
+        /// </summary>
+        Task<string> ExtractAsync(
+            Stream fileStream,
+            string mimeType,
+            CancellationToken cancellationToken = default
+        );
+    }
+}

Interfaces/Extractors/IXPdfFileContentExtractor.cs

@@ -0,0 +1,5 @@
+namespace xAiApi.Interfaces.Extractors
+{
+    public interface IXPdfFileContentExtractor : IXFileContentExtractor
+    { }
+}

Interfaces/Extractors/IXPlainTextFileContentExtractor.cs

@@ -0,0 +1,5 @@
+namespace xAiApi.Interfaces.Extractors
+{
+    public interface IXPlainTextFileContentExtractor : IXFileContentExtractor
+    { }
+}