fix: resolve npm audit vulnerabilities via overrides

Add npm overrides to force mocha's transitive dependencies to patched
versions:
- diff ^7.0.0 -> ^8.0.3 (fixes GHSA-73rr-hh4g-fpgx DoS)
- serialize-javascript ^6.0.2 -> ^7.0.5 (fixes GHSA-5c6j-r48x-rmvq
  RCE, GHSA-qj8w-gfj5-8c6v DoS)

npm audit now reports 0 vulnerabilities. All 162 tests pass.

Closes #37

Signed-off-by: Sebastien Tardif <sebtardif@ncf.ca>

Author: SebTardif

package-lock.json

@@ -130,6 +130,12 @@
     "package": "vsce package",
     "check": "npm run test && npm run package"
   },
+  "overrides": {
+    "mocha": {
+      "diff": "^8.0.3",
+      "serialize-javascript": "^7.0.5"
+    }
+  },
   "devDependencies": {
     "@types/mocha": "^10.0.10",
     "@types/node": "^25.9.1",