### What this PR does / why we need it?
Add import_kernels interface to avoid import useless vLLM C library
Closes#3488. Reopen#3498 for CI.
### How was this patch tested?
CI tested.
- vLLM version: v0.11.0
- vLLM main:
2918c1b49c
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Signed-off-by: gcanlin <canlinguosdu@gmail.com>