rebase: adapt to vLLM 0.29 callback, embedding and video decoder changes

Four unrelated 0.29 surface changes, each reproduced locally against the
pinned f5c3cc24 build:

- PromptUpdateDetails.is_embed now takes only the full token list. The
  Bagel img2img replacement still declared (tok, seq), which crashed
  stage-0 engine core startup and produced the Distributed and Qwen3-Omni
  "no live replica" failures rather than anything KV related.

- dispatch_unquantized_gemm gained a linear_backend argument and is called
  with it. The CPU-forcing test stubs took no arguments; they now accept
  and ignore whatever upstream passes so a further signature change does
  not break them again.

- VocabParallelEmbedding gained a fused kernel that engages whenever
  tp_size > 1 on CUDA, and it has no CPU implementation. The encoder TP
  fixtures drive CPU tensors under a faked TP group, so they pin the
  portable masked path.

- The pyav video decoder backend was removed; valid options are now
  opencv, torchcodec, pynvvideocodec and deepstream. The OpenAI video
  endpoint hardcoded pyav, which turned every video request into a 400.
  It moves to opencv, the upstream default.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0146Xu5Sgj4vXxLxvLjV5YPj
Signed-off-by: tzhouam <tzhouam@connect.ust.hk>

tests/diffusion/models/glm_image/test_glm_image_quantization.py

@@ -69,7 +69,7 @@ def _force_default_gemm(monkeypatch):
 
     monkeypatch.setattr(
         "vllm.model_executor.layers.linear.dispatch_unquantized_gemm",
-        lambda: default_unquantized_gemm,
+        lambda *_args, **_kwargs: default_unquantized_gemm,
     )