fix(ffi): reject resizable buffers in nonblocking calls (#36259)
## Summary
- validate retained V8 backing stores before dispatching nonblocking FFI
calls
- reject user-resizable stores for buffer arguments, struct arguments,
and result storage
- preserve synchronous FFI behavior and fixed-buffer support
## Background
Nonblocking FFI calls retain a backing-store reference and pass its data
pointer to a worker thread. The reference keeps the backing-store object
alive, but a user-resizable store can still change its data pointer
after the call is dispatched.
The nonblocking path now accepts only fixed backing stores before
retaining and forwarding their pointers. This applies consistently to
direct `ArrayBuffer` values, views, nested struct inputs, and the
internal storage used for struct results.
## Tests
- `cargo test -p deno_ffi`
- `cargo build -p deno -p test_server -p test_ffi`
- `cargo test -p integration_tests --test integration ffi::ffi_basic`
- `cargo clippy -p deno_ffi --all-targets -- -D warnings`
- `./tools/format.js ext/ffi/ir.rs ext/ffi/call.rs
tests/ffi/testdata/test.js`
