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/.gitignore

@@ -0,0 +1,25 @@
+# BenchmarkDotNet artifacts
+BenchmarkDotNet.Artifacts/
+
+# Test images generated during benchmarks
+TestImages/
+
+# Build outputs
+bin/
+obj/
+
+# User-specific files
+*.suo
+*.user
+*.userosscache
+*.sln.docstates
+
+# Results and logs
+*.log
+*.html
+*.csv
+results/
+
+# Temporary files
+*.tmp
+*.temp