feat: enable processing of large video files over 2GB

Update audio extraction to use file-based streaming
instead of in-memory buffers to support processing
video files larger than 2GB.

**Changes:**
- Modified `IAudioExtractor.ExtractMp3FromMp4Async()`
  to accept an output audio stream parameter instead
  of creating a MemoryStream internally
- Updated `AudioExtractor` to write directly to the
  provided audio stream, eliminating the need to load
  entire video into memory
- Enhanced `FFMpegService` to detect FileStream inputs
  and use direct file-to-file processing when possible,
  falling back to pipe-based streaming for other stream types
- Refactored `DefaultCommand` to create output directory
  and audio file stream before extraction, enabling direct
  file-based audio extraction
- Updated all unit and integration tests to accommodate the
  new audio stream parameter

This change prevents `OutOfMemoryException` errors when processing
large video files by streaming data directly to disk rather than
buffering in memory. Additionally, it removes the possibility of
overflowing the 2GB size limit that `MemoryStream` has, which
would result in `IOException` errors when trying to write or
copy to it.

tests/StreamShorts.Library.Tests/Integration/Media/Audio/AudioExtractorTests.cs

@@ -9,13 +9,15 @@ public class AudioExtractorTests
   {
     using var testVideo = TestData.GetTestVideo();
     using var extractedAudio = TestData.GetExtractedAudio();
+    using var audioStream = new MemoryStream();
 
-    var result = await _sut.ExtractMp3FromMp4Async(testVideo);
+    var result = await _sut.ExtractMp3FromMp4Async(testVideo, audioStream);
 
     var audioBytes = await ConvertStreamToBytesAsync(extractedAudio);
     var resultBytes = await ConvertStreamToBytesAsync(result);
 
     resultBytes.Should().Equal(audioBytes);
+    result.Should().BeSameAs(audioStream);
   }
 
   private static async Task<byte[]> ConvertStreamToBytesAsync(Stream stream)