Add sleep mode feature for Ascend NPU (#513)

### What this PR does / why we need it?
This PR adds sleep mode feature for vllm-ascend, when sleeps, we do
mainly two things:

- offload model weights
- discard kv cache

RLHF tools(such as https://github.com/volcengine/verl and
https://github.com/OpenRLHF/OpenRLHF) have a strong need of sleep mode
to accelerate the training process.

This PR may solve #375 and #320 .

### Does this PR introduce _any_ user-facing change?
No existing user interfaces changed.
Users will have two new methods(`sleep()` and `wake_up()`) to use.

### How was this patch tested?
This PR is tested with Qwen/Qwen2.5-0.5B-Instruct.

At first, we have free NPU memory M1.

After `llm = LLM("Qwen/Qwen2.5-0.5B-Instruct", enable_sleep_mode=True)`
executed, we have free NPU memory M2. M2 < M1.

Then we call `llm.sleep(level=1)`, we have free NPU memory M3.

We have M3 > M2, M3 is very close to M1.

Plus, we have the same output tokens before sleep and after wake up,
with the config of `SamplingParams(temperature=0, max_tokens=10)` and
with the same input tokens of course.


This PR is utilizing the CMake procedure of #371 , thanks a lot.

Signed-off-by: Shuqiao Li <celestialli@outlook.com>

setup.py

@@ -123,6 +123,10 @@ class cmake_build_ext(build_ext):
         cmake_args += [f"-DCMAKE_BUILD_TYPE={envs.CMAKE_BUILD_TYPE}"]
         # Default dump the compile commands for lsp
         cmake_args += ["-DCMAKE_EXPORT_COMPILE_COMMANDS=1"]
+        if envs.CXX_COMPILER is not None:
+            cmake_args += [f"-DCMAKE_CXX_COMPILER={envs.CXX_COMPILER}"]
+        if envs.C_COMPILER is not None:
+            cmake_args += [f"-DCMAKE_C_COMPILER={envs.C_COMPILER}"]
         if envs.VERBOSE:
             cmake_args += ["-DCMAKE_VERBOSE_MAKEFILE=ON"]