Use Vector256<float>.Count instead of magic 8

src/ImageSharp/Formats/Jpeg/Components/Decoder/ColorConverters/JpegColorConverter.FromCmykAvx.cs

@@ -32,7 +32,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
                 // Used for the color conversion
                 var scale = Vector256.Create(1 / this.MaximumValue);
 
-                nint n = values.Component0.Length / 8;
+                nint n = values.Component0.Length / Vector256<float>.Count;
                 for (nint i = 0; i < n; i++)
                 {
                     ref Vector256<float> c = ref Unsafe.Add(ref c0Base, i);

src/ImageSharp/Formats/Jpeg/Components/Decoder/ColorConverters/JpegColorConverter.FromGrayScaleAvx.cs

@@ -26,7 +26,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
                 // Used for the color conversion
                 var scale = Vector256.Create(1 / this.MaximumValue);
 
-                nint n = values.Component0.Length / 8;
+                nint n = values.Component0.Length / Vector256<float>.Count;
                 for (nint i = 0; i < n; i++)
                 {
                     ref Vector256<float> c0 = ref Unsafe.Add(ref c0Base, i);

src/ImageSharp/Formats/Jpeg/Components/Decoder/ColorConverters/JpegColorConverter.FromRgbAvx.cs

@@ -29,7 +29,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
 
                 // Used for the color conversion
                 var scale = Vector256.Create(1 / this.MaximumValue);
-                nint n = values.Component0.Length / 8;
+                nint n = values.Component0.Length / Vector256<float>.Count;
                 for (nint i = 0; i < n; i++)
                 {
                     ref Vector256<float> r = ref Unsafe.Add(ref rBase, i);

src/ImageSharp/Formats/Jpeg/Components/Decoder/ColorConverters/JpegColorConverter.FromYCbCrAvx.cs

@@ -38,7 +38,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
                 var bCbMult = Vector256.Create(FromYCbCrScalar.BCbMult);
 
                 // Walking 8 elements at one step:
-                nint n = values.Component0.Length / 8;
+                nint n = values.Component0.Length / Vector256<float>.Count;
                 for (nint i = 0; i < n; i++)
                 {
                     // y = yVals[i];

src/ImageSharp/Formats/Jpeg/Components/Decoder/ColorConverters/JpegColorConverter.FromYccKAvx.cs

@@ -40,7 +40,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.ColorConverters
                 var bCbMult = Vector256.Create(FromYCbCrScalar.BCbMult);
 
                 // Walking 8 elements at one step:
-                nint n = values.Component0.Length / 8;
+                nint n = values.Component0.Length / Vector256<float>.Count;
                 for (nint i = 0; i < n; i++)
                 {
                     // y = yVals[i];