fix(docker): have already the converter in the docker image

cmd/encoder-setup/main.go

@@ -0,0 +1,19 @@
+//go:build encoder_setup
+// +build encoder_setup
+
+package main
+
+import (
+	"fmt"
+	"log"
+
+	"github.com/belphemur/CBZOptimizer/v2/pkg/converter/webp"
+)
+
+func main() {
+	fmt.Println("Setting up WebP encoder for tests...")
+	if err := webp.PrepareEncoder(); err != nil {
+		log.Fatalf("Failed to prepare WebP encoder: %v", err)
+	}
+	fmt.Println("WebP encoder setup complete.")
+}