[Feature] Sfa/MRV2 pcp support (#14026)

### What this PR does / why we need it?
SFA PCP Implementation: Introduced AscendSFACPMetadata and
AscendSFACPImpl to handle Prefill Context Parallelism (PCP) logic for
Sparse Flash Attention.
Indexer Backend Updates: Updated AscendSFAIndexerBackend to support PCP
and marked it as a cache-only backend.
PCP Manager Integration: Added a new patch for the PCP manager to ensure
compatibility with the vLLM worker and proper integration.
Graph Capture and Partitioning: Modified aclgraph_utils and pcp_manager
to support PCP-local input partitioning and ensure CUDA graph capture
binds to correct buffers.
Configuration Validation: Added strict configuration validation in
pcp_manager to enforce graph-safe PCP execution on Ascend NPUs.
### Does this PR introduce _any_ user-facing change?
NO
### How was this patch tested?


- vLLM version: v0.27.1
- vLLM main:
https://github.com/vllm-project/vllm/commit/ba07e4a48fc951300d97eb506217dd530583dea3

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