vm2: timeout Option Bypass via FinalizationRegistry Cleanup Callback (Unbounded Host Event-Loop Block)

### Vulnerability Summary vm2's `VM({ timeout })` option is documented and relied upon as the mechanism that bounds how long sandboxed code may execute. In the current implementation, the timeout only wraps the single synchronous call to `VM#run()` (via `doWithTimeout` → `this._runScript(script)` in `lib/vm.js`). It does not, and structurally cannot, bound code that the V8 engine itself schedules to run *after* that call has already returned. `FinalizationRegistry` and `WeakRef` are exposed to sandboxed code completely unmodified — they are not present anywhere in `lib/setup-sandbox.js`'s list of specially-wrapped/hardened globals (only `WeakMap`, `Promise`, `Proxy`, `Reflect`, etc. receive hardening there). Sandboxed code can register a `FinalizationRegistry` callback against an object it creates and immediately drops. `VM#run()` returns normally, well within the configured timeout, because registration is instant. At some later point — determined entirely by the V8 garbage collector, and forceable on demand by the host process (e.g. under memory pressure, or via `--expose-gc`) — the engine invokes the sandboxed cleanup callback directly. This invocation is **not** mediated by `doWithTimeout`, `Script.runInContext({timeout})`, or any other vm2 accounting mechanism, because it isn't a new call to `VM#run()` at all — it's the GC's own native callback-invocation path. ## Affected Code & Version - **Repository:** `patriksimek/vm2` - **Version tested:** `3.11.6` (commit `a5b31cd9