Added factory method to create combined stream from IEnumerable<Stream> (#255)

Author: sakno

src/DotNext.IO/IO/StreamExtensions.cs

@@ -3,7 +3,8 @@
 
 namespace DotNext.IO;
 
-using Collections.Generic;
+using Buffers;
+using static Runtime.Intrinsics;
 
 /// <summary>
 /// Represents high-level read/write methods for the stream.
@@ -58,8 +59,23 @@ public static Stream Combine(this ReadOnlySpan<Stream> streams)
     /// <exception cref="ArgumentException"><paramref name="streams"/> is empty.</exception>
     public static Stream Combine(this IEnumerable<Stream> streams)
     {
-        using var buffer = streams.Copy();
-        return Combine(buffer.Span);
+        // Use buffer to allocate streams on the stack
+        var buffer = new StreamBuffer();
+        var writer = new BufferWriterSlim<Stream>(buffer);
+
+        Stream result;
+        try
+        {
+            writer.AddAll(streams);
+            result = Combine(writer.WrittenSpan);
+        }
+        finally
+        {
+            writer.Dispose();
+            KeepAlive(in buffer);
+        }
+
+        return result;
     }
 
     /// <summary>
@@ -81,4 +97,10 @@ public static Stream AsUnbufferedStream(this SafeFileHandle handle, FileAccess a
             ? new UnbufferedFileStream(handle, access)
             : throw new ArgumentException(ExceptionMessages.FileHandleClosed, nameof(handle));
     }
+    
+    [InlineArray(32)]
+    private struct StreamBuffer
+    {
+        private Stream element0;
+    }
 }

src/DotNext/Buffers/BufferWriterSlim.cs

@@ -358,7 +358,7 @@ public void Clear(bool reuseBuffer = false)
     /// </summary>
     /// <param name="collection">A collection of elements.</param>
     /// <exception cref="ArgumentNullException"><paramref name="collection"/> is <see langword="null"/>.</exception>
-    public void Write(IEnumerable<T> collection)
+    public void AddAll(IEnumerable<T> collection)
     {
         ArgumentNullException.ThrowIfNull(collection);