Reserve space for std::vector output in extract_tensors for nccl python bindings (#88203)
Optimizes the nccl python bindings to reserve space when converting PythonObject* into Tensors. This should reduce the number of unnecessary allocations in the nccl bindings as the std::vector grows.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/88203
Approved by: https://github.com/ezyang
