Change AddSinglePixOrCopy to accept 'in PixOrCopy'

src/ImageSharp/Formats/Webp/Lossless/CostModel.cs

@@ -42,7 +42,7 @@ internal class CostModel
         // The following code is similar to HistogramCreate but converts the distance to plane code.
         foreach (PixOrCopy v in backwardRefs)
         {
-            histogram.AddSinglePixOrCopy(v, true, xSize);
+            histogram.AddSinglePixOrCopy(in v, true, xSize);
         }
 
         ConvertPopulationCountTableToBitEstimates(histogram.NumCodes(), histogram.Literal, this.Literal);

src/ImageSharp/Formats/Webp/Lossless/HistogramEncoder.cs

@@ -113,7 +113,7 @@ internal static class HistogramEncoder
         foreach (PixOrCopy v in backwardRefs)
         {
             int ix = ((y >> histoBits) * histoXSize) + (x >> histoBits);
-            histograms[ix].AddSinglePixOrCopy(v, false);
+            histograms[ix].AddSinglePixOrCopy(in v, false);
             x += v.Len;
             while (x >= xSize)
             {

src/ImageSharp/Formats/Webp/Lossless/Vp8LHistogram.cs

@@ -140,7 +140,7 @@ internal abstract unsafe class Vp8LHistogram
     {
         foreach (PixOrCopy v in refs)
         {
-            this.AddSinglePixOrCopy(v, false);
+            this.AddSinglePixOrCopy(in v, false);
         }
     }
 
@@ -150,7 +150,7 @@ internal abstract unsafe class Vp8LHistogram
     /// <param name="v">The token to add.</param>
     /// <param name="useDistanceModifier">Indicates whether to use the distance modifier.</param>
     /// <param name="xSize">xSize is only used when useDistanceModifier is true.</param>
-    public void AddSinglePixOrCopy(PixOrCopy v, bool useDistanceModifier, int xSize = 0)
+    public void AddSinglePixOrCopy(in PixOrCopy v, bool useDistanceModifier, int xSize = 0)
     {
         if (v.IsLiteral())
         {