[HybridKV] Fix prefill disaggregation kvcache addr alignment & use hybrid kv cache only when running qwen3_next (#3007)

### What this PR does / why we need it?
This pr fixes a few issues on prefill disaggregation:
1. Fix prefill disaggregation kvcache addr alignment issue, llmdatadist
needs the addr of tensors to be aligned with 2M
2. Fix prefill disaggregation kvcache shape error, llmdatadist requires
k/v tensors with shape [num_blocks, ...], however the implentment before
this pr is [2, num_blocks, ...], which will break prefill disaggregation
3. Use hybrid kv cache only when running qwen3_next to fix accuracy
issue on prefill disaggregation.

### Does this PR introduce _any_ user-facing change?
N/A

### How was this patch tested?
Tested locally by @liziyu179 

- vLLM version: v0.10.2
- vLLM main:
4f02b77de4

---------

Signed-off-by: MengqingCao <cmq0113@163.com>

vllm_ascend/platform.py

@@ -25,7 +25,6 @@ from torch.distributed import ProcessGroup
 from torch.distributed.distributed_c10d import PrefixStore
 from vllm.logger import logger
 from vllm.platforms import Platform, PlatformEnum
-from vllm.utils import cdiv
 
 from vllm_ascend.ascend_config import (check_ascend_config, get_ascend_config,
                                        init_ascend_config)
@@ -247,10 +246,6 @@ class NPUPlatform(Platform):
         if cache_config:
             if cache_config.block_size is None:
                 cache_config.block_size = 128
-            else:
-                if not vllm_config.model_config.is_deepseek_mla:
-                    cache_config.block_size = cdiv(cache_config.block_size,
-                                                   64) * 64
 
             if cache_config.enable_prefix_caching and cache_config.block_size != 128:
                 logger.warning(