[Misc] Remove redundant ClassRegistry (#29681)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>
Signed-off-by: Cyrus Leung <cyrus.tl.leung@gmail.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

vllm/model_executor/models/interfaces.py

@@ -32,11 +32,13 @@ if TYPE_CHECKING:
     from vllm.config import VllmConfig
     from vllm.model_executor.models.utils import WeightsMapper
     from vllm.multimodal.inputs import MultiModalFeatureSpec
+    from vllm.multimodal.registry import _ProcessorFactories
     from vllm.sequence import IntermediateTensors
 else:
     VllmConfig = object
     WeightsMapper = object
     MultiModalFeatureSpec = object
+    _ProcessorFactories = object
     IntermediateTensors = object
 
 logger = init_logger(__name__)
@@ -87,6 +89,11 @@ class SupportsMultiModal(Protocol):
     A set indicating CPU-only multimodal fields.
     """
 
+    _processor_factory: ClassVar[_ProcessorFactories]
+    """
+    Set internally by `MultiModalRegistry.register_processor`.
+    """
+
     @classmethod
     def get_placeholder_str(cls, modality: str, i: int) -> str | None:
         """