fix: guard FuturePromise resolve against env teardown crash

[cam-from-ditto]

Summary

• Mirrors #1 (the napi_delete_async_work env-teardown fix) but for the TSFN-backed FuturePromise used by Env::execute_tokio_future.
• Registers a napi_add_env_cleanup_hook per FuturePromise to detect when the N-API environment begins tearing down. When set, the TSFN's call_js_cb skips napi_resolve_deferred / napi_reject_deferred to avoid crashing inside V8's GlobalHandles::Destroy.
• The cleanup hook is unregistered on normal completion so it doesn't leak.

Root cause

In Node.js >= 22, the Persistent<Promise::Resolver> backing the Deferred can be invalidated during environment teardown before the TSFN's queued AsyncCb fires. When the AsyncCb then calls napi_resolve_deferred, V8's GlobalHandles::Destroy segfaults on the dangling handle.

This is the trace that DEVX-852 was originally chasing:

#0  v8::internal::GlobalHandles::Destroy(unsigned long*)         ← SIGSEGV
#1  napi_resolve_deferred()
#2  call_js_cb<...>()                napi-rs/promise.rs:111
#3  v8impl::ThreadSafeFunction::AsyncCb(uv_async_s*)
#4  uv__async_io
...

Frame 2 is the function this PR guards.

Validation

CI run 25482278460 on getditto/ditto's cam/DEVX-852/flaky-node-v24-sigsegv branch (which has both this fix and the previously-merged napi_delete_async_work fix) no longer hits the original signature. A different unrelated crash now surfaces (node::fs::FSReqPromise::~FSReqPromise from Node's own fs internals), confirming this PR closes its target trace.

Test plan

• Sanity-check CI on the consumer (getditto/ditto) once this is merged and Cargo.lock is bumped.