BREAKING CHANGE(smartpdf): improve image generation quality and API consistency

- Renamed convertPDFToWebpPreviews to convertPDFToWebpBytes for consistency
- Added configurable scale options with DPI support
- Changed default scale to 3.0 (216 DPI) for better quality
- Added DPI helper methods and scale constants

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@push.rocks/smartpdf",
-  "version": "3.3.0",
+  "version": "4.0.0",
   "private": false,
   "description": "A library for creating PDFs dynamically from HTML or websites with additional features like merging PDFs.",
   "main": "dist_ts/index.js",