vm2: `allowAsync: false` can be bypassed through Promise thenable assimilation in VM and NodeVM

### Summary When `allowAsync` is set to `false`, vm2 is expected to reject attempts to run asynchronous code. Direct use of `Promise.prototype.then` is blocked, but Promise static methods still assimilate attacker-controlled thenables. `Promise.resolve(thenable)`, `Promise.all([thenable])`, `Promise.race([thenable])`, `Promise.any([thenable])`, and `Promise.allSettled([thenable])` can invoke the thenable's `then` method in a microtask after `VM.run()` or `NodeVM.run()` has already returned. This bypasses the documented async-execution restriction and runs outside the configured `timeout`, allowing sandboxed code to continue executing after the host believes execution is complete. ### Details The documented VM option says `allowAsync: false` should cause attempts to run async code to throw a `VMError`; README.md:139-145 also recommends using it with `timeout`. The implementation enforces part of this policy by replacing `localPromise.prototype.then` with an `AsyncErrorHandler` when async is disabled: - `lib/setup-sandbox.js:1629-1637` defines `AsyncErrorHandler`, whose `apply` and `construct` traps throw `VMError: Async not available`. - `lib/setup-sandbox.js:1743-1752` installs that handler on `localPromise.prototype.then` when `allowAsync` is false. However, Promise static methods are still exposed and rebound to `localPromise`: - `lib/setup-sandbox.js:1816-1819` wraps `Promise.all`. - `lib/setup-sandbox.js:1821-1824` wraps `Promise.race`. - `lib/setup-sandbox.js:1826-1830`