Unexpected Performance Drop Caused by Explicit deep_ep.Buffer Memory Release

## Problem description

Currently, we explicitly release `deep_ep.Buffer` by calling `del buffer` and setting `buffer = None` in order to free device memory:

```python
buffer = deep_ep.Buffer(
group,
int(2e9),
int(1e9),
low_latency_mode=args.test_ll_compatibility,
num_qps_per_rank=num_qps_per_rank,
explicitly_destroy=False,
)
assert num_local_ranks == 8 and num_ranks > 8

del buffer
buffer = None
```
However, this approach forces the buffer to be fully re-created every time it is used again. After upgrading to a newer NVSHMEM version, this repeated creation and destruction introduces a noticeable performance regression, likely due to the increased overhead in buffer initialization and NVSHMEM internal setup.

We would like to know:

- Is there a recommended way to explicitly release or recycle deep_ep.Buffer memory without destroying the entire buffer object?
- Are there any best practices when using deep_ep.Buffer with newer NVSHMEM versions to mitigate this performance drop?

Any guidance or suggestions would be greatly appreciated.