model: TP-wide single-owner image encoding for DeepSeek V4.1

ViT and Aligner are replicated per TP rank, encoding each image eight
times with TP8 on both CP1 and CP8. Elect one owner per image and use
ordered full-span broadcasts with a six-phase agreement protocol.
Both CP1 and CP8 benefit while local cache hits preserve collective order.

test/registered/unit/models/test_deepseek_v41_vision_cp_inputs.py

@@ -77,6 +77,7 @@ class _VisionStub(DeepseekV4ForCausalLM):
         self.config = SimpleNamespace(image_token_id=IMAGE_TOKEN_ID)
         self.vision = object()
         self.tp_size = 1
+        self.mm_owner_group = None
         self.model = _RecordingBody(embed)
         self.pp_group = SimpleNamespace(is_last_rank=True)
         self.lm_head = object()