feat: add datVerifier and tests

- Añade `datVerifier` con `parseDat` y `verifyHashesAgainstDat`
- Añade tests y fixture XML para validar matching por CRC/MD5/SHA1/size
- Añade `fast-xml-parser` en `backend/package.json` (devDependency)

backend/package.json

@@ -30,6 +30,7 @@
   "devDependencies": {
     "@types/node": "^18.0.0",
     "eslint": "^8.0.0",
+    "fast-xml-parser": "^5.3.5",
     "prettier": "^2.8.0",
     "prisma": "6.19.2",
     "ts-node-dev": "^2.0.0",