Add image processing benchmarks and UI folder open buttons

- Added MaddoShared.Benchmarks project with BenchmarkDotNet for comprehensive image processing performance tests (parallel, chunk, size, stress).
- Included helper for generating test images and custom configs to ensure InProcess toolchain for .NET Windows compatibility.
- Added cross-platform scripts to run benchmarks easily.
- Updated .gitignore for benchmark artifacts and temp files.
- Exposed GetFilesToProcessPublic in ImageCreationStuff for testability.
- Added file name sanitization in ImageCreatorSharp to prevent IO errors.
- Enhanced WinForms UI: added "Open" buttons for source/destination folders, handled folder opening in Explorer, and improved user messaging and layout.
- Updated solution file to include new benchmark project.

MaddoShared.Benchmarks/Helpers/TestImageGenerator.cs

@@ -0,0 +1,107 @@
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Drawing;
+using System.Drawing.Imaging;
+using System.IO;
+
+namespace MaddoShared.Benchmarks.Helpers;
+
+/// <summary>
+/// Helper class to generate test images for benchmarking
+/// </summary>
+[SuppressMessage("Interoperability", "CA1416:Validate platform compatibility")]
+public static class TestImageGenerator
+{
+    /// <summary>
+    /// Generates a set of test JPEG images in the specified directory
+    /// </summary>
+    /// <param name="outputDirectory">Directory where images will be created</param>
+    /// <param name="imageCount">Number of images to generate</param>
+    /// <param name="width">Width of each image</param>
+    /// <param name="height">Height of each image</param>
+    /// <param name="includeSubfolders">Whether to create images in subfolders</param>
+    public static void GenerateTestImages(
+        string outputDirectory, 
+        int imageCount, 
+        int width = 4000, 
+        int height = 3000,
+        bool includeSubfolders = false)
+    {
+        Directory.CreateDirectory(outputDirectory);
+
+        var random = new Random(42); // Fixed seed for reproducibility
+
+        for (int i = 0; i < imageCount; i++)
+        {
+            var targetDir = outputDirectory;
+            
+            if (includeSubfolders && i % 10 == 0)
+            {
+                targetDir = Path.Combine(outputDirectory, $"Subfolder_{i / 10}");
+                Directory.CreateDirectory(targetDir);
+            }
+
+            var filePath = Path.Combine(targetDir, $"test_image_{i:D5}.jpg");
+            
+            // Skip if already exists
+            if (File.Exists(filePath))
+                continue;
+
+            using var bitmap = new Bitmap(width, height);
+            using var graphics = Graphics.FromImage(bitmap);
+            
+            // Fill with a random color background
+            var bgColor = Color.FromArgb(random.Next(256), random.Next(256), random.Next(256));
+            graphics.Clear(bgColor);
+
+            // Draw some random shapes to make it more realistic
+            for (int j = 0; j < 20; j++)
+            {
+                var color = Color.FromArgb(random.Next(256), random.Next(256), random.Next(256));
+                var brush = new SolidBrush(color);
+                var x = random.Next(width);
+                var y = random.Next(height);
+                var w = random.Next(200, 800);
+                var h = random.Next(200, 800);
+                graphics.FillEllipse(brush, x, y, w, h);
+            }
+
+            // Add some text
+            using var font = new Font("Arial", 48, FontStyle.Bold);
+            var text = $"Test Image {i}";
+            var textBrush = new SolidBrush(Color.White);
+            graphics.DrawString(text, font, textBrush, new PointF(100, 100));
+
+            // Save as JPEG with standard quality
+            var encoder = GetEncoder(ImageFormat.Jpeg);
+            var encoderParameters = new EncoderParameters(1);
+            encoderParameters.Param[0] = new EncoderParameter(Encoder.Quality, 85L);
+            
+            bitmap.Save(filePath, encoder, encoderParameters);
+        }
+    }
+
+    /// <summary>
+    /// Cleans up generated test images
+    /// </summary>
+    public static void CleanupTestImages(string directory)
+    {
+        if (Directory.Exists(directory))
+        {
+            Directory.Delete(directory, recursive: true);
+        }
+    }
+
+    private static ImageCodecInfo GetEncoder(ImageFormat format)
+    {
+        var codecs = ImageCodecInfo.GetImageEncoders();
+        foreach (var codec in codecs)
+        {
+            if (codec.FormatID == format.Guid)
+            {
+                return codec;
+            }
+        }
+        return null;
+    }
+}