Use no compression for created entries (#43)

Replace CompressionLevel.Fastest with CompressionLevel.NoCompression when creating archive entries. This avoids compression-related variability and helps ensure deterministic output (while keeping LastWriteTime set to StableDateOffset).

Author: SimonCropp

src/DeterministicIoPackaging/DeterministicPackage.cs

@@ -103,7 +103,7 @@ static void SaveXml(XDocument xml, Stream targetStream) =>
 
     static Entry CreateEntry(Entry source, Archive target)
     {
-        var entry = target.CreateEntry(source.FullName, CompressionLevel.Fastest);
+        var entry = target.CreateEntry(source.FullName, CompressionLevel.NoCompression);
         entry.LastWriteTime = StableDateOffset;
         return entry;
     }