refactor: replace fileutil with fsutil and local hashing

internal/fsutil/fsutil.go

@@ -0,0 +1,32 @@
+package fsutil
+
+import (
+	"fmt"
+	"os"
+)
+
+func EnsureDir(path string) error {
+	info, err := os.Stat(path)
+	if os.IsNotExist(err) {
+		return os.MkdirAll(path, 0755)
+	}
+	if err != nil {
+		return err
+	}
+	if !info.IsDir() {
+		return fmt.Errorf("file already exists at %s", path)
+	}
+	return nil
+}
+
+func Exists(path string) bool {
+	info, err := os.Stat(path)
+	return err == nil && !info.IsDir()
+}
+
+func Remove(path string) error {
+	if !Exists(path) {
+		return nil
+	}
+	return os.Remove(path)
+}