### What this PR does / why we need it?
In certain scenarios, the performance of synchronously loading data from
the pool is better than that of asynchronously loading data. Therefore,
a control logic (or switch) for asynchronous loading from the pool has
been added.
### Does this PR introduce _any_ user-facing change?
### How was this patch tested?
- vLLM version: v0.11.0rc3
- vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.0
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