[Misc] Fix import error and address nits to make CI happy (#563)

1. Add `vllm_version_is` function to check vllm version.
2. `ensure_kv_transfer_initialized` and `get_kv_transfer_group ` have
been moved to other place in vllm main branch via
3408e47159
, this patch fix the import error.

Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>

.github/workflows/mypy.yaml

@@ -47,7 +47,7 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies
       run: |
-        pip install -r requirements-dev.txt 
+        pip install -r requirements-dev.txt
 
     - name: Checkout vllm-project/vllm repo
       uses: actions/checkout@v4