Exit 13 on unsettled top-level await in the main entry instead of spinning - #36051

The new Pending check fires whenever `is_event_loop_alive()` returned false, but that function also returns false when `unhandled_error_counter > 0` (VirtualMachine.rs:1036) — i.e. the wait was aborted by a fatal uncaught exception, not a natural drain. In that case ref'd handles that would have settled the entry promise are still live, so the "Detected unsettled top-level await" warning is spurious and misattributes the failure (Node prints only the exception). Gate this block on `vm.unhandled_

The `SAFETY: p is a live JSC heap cell tracked by the VM` comment is false — in the non-watcher path `pending_internal_promise` is stored with `is_protected = false` and only `ensure_still_alive()` (frame-local `black_box`), and no C++ `visitChildren` visits it. This deref runs after the stack local dies at line 1530, after `run_gc(false)` at 1540, the drain loop, and `on_before_exit()`'s inner tick loop; once the entry promise settles it is reachable only from this unrooted raw pointer, so GC c

The new `!is_event_loop_alive()` break regresses `p.unref(); await p.exited` — an unref'd subprocess doesn't count toward liveness, so the loop bails before `auto_tick()` ever pumps the OS loop, the entry await stays Pending, and the process exits 13 with the warning instead of resolving. This is failing `test/js/bun/spawn/spawn.test.ts:805-840` ("unref() + .exited with nothing else ref'd") on **all 8 CI platforms** per the robobun comment. Either narrow the check so an in-flight unref'd child s