fix: properly include lantern/testing in build

Removed the exclusion of `lantern/testing` from tsconfig and fixed the
underlying TypeScript errors by:
- Installing @types/mocha for Mocha type definitions
- Creating stub type declarations for chrome-devtools testing utilities

The directory is now properly compiled without errors instead of being
hidden via exclusion.

Fixes the build without bypassing type checking.

Author: mithun50

package-lock.json

@@ -49,6 +49,7 @@
     "@stylistic/eslint-plugin": "^5.4.0",
     "@types/debug": "^4.1.12",
     "@types/filesystem": "^0.0.36",
+    "@types/mocha": "^10.0.10",
     "@types/node": "^24.3.3",
     "@types/sinon": "^17.0.4",
     "@types/yargs": "^17.0.33",

package.json

@@ -58,7 +58,6 @@
     "node_modules/chrome-devtools-frontend/front_end/third_party/third-party-web"
   ],
   "exclude": [
-    "node_modules/chrome-devtools-frontend/**/*.test.ts",
-    "node_modules/chrome-devtools-frontend/front_end/models/trace/lantern/testing"
+    "node_modules/chrome-devtools-frontend/**/*.test.ts"
   ]
 }