[aclgraph] implentment NPUPiecewiseBackend to enable aclgraph (#836)

### What this PR does / why we need it?
1. Implentment `NPUPiecewiseBackend` to enable aclgraph
2. Eable aclgraph by default in V1, but raise error when running
deepseek and raise warning when running models except for qwen

### How was this patch tested?
CI pass with the new ut

---------

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

tests/conftest.py

@@ -77,7 +77,7 @@ class VllmRunner:
         block_size: int = 16,
         enable_chunked_prefill: bool = False,
         swap_space: int = 4,
-        enforce_eager: Optional[bool] = False,
+        enforce_eager: Optional[bool] = True,
         **kwargs,
     ) -> None:
         self.model = LLM(