[mypy] Enable type checking for more directories (#29674)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

vllm/triton_utils/__init__.py

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+from typing import TYPE_CHECKING
 
 from vllm.triton_utils.importing import (
     HAS_TRITON,
@@ -7,7 +8,7 @@ from vllm.triton_utils.importing import (
     TritonPlaceholder,
 )
 
-if HAS_TRITON:
+if TYPE_CHECKING or HAS_TRITON:
     import triton
     import triton.language as tl
     import triton.language.extra.libdevice as tldevice