chore: add c8 for coverage

Author: matteo-gobbo

package.json

@@ -9,6 +9,7 @@
     "@fastify/busboy": "^3.0.0",
     "@fastify/deepmerge": "^2.0.0",
     "@fastify/error": "^4.0.0",
+    "c8": "^10.1.3",
     "fastify-plugin": "^5.0.0",
     "secure-json-parse": "^3.0.0"
   },
@@ -31,14 +32,13 @@
     "tsd": "^0.31.0"
   },
   "scripts": {
-    "coverage": "npm run test:unit -- --coverage-report=html",
     "climem": "climem 8999 localhost",
     "lint": "eslint",
     "lint:fix": "eslint --fix",
     "start": "CLIMEM=8999 node -r climem ./examples/example",
     "test": "npm run test:unit && npm run test:typescript",
     "test:typescript": "tsd",
-    "test:unit": "node --test"
+    "test:unit": "c8 --100 node --test"
   },
   "repository": {
     "type": "git",