[model, megatron] feat: Support for Qwen3VL dense models

[HollowMan6]

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Qwen3VL dense models support have already been added to mbridge: ISEEKYAN/mbridge#33

I've also tested it using the MoE script (but with MoE related stuff removed) and it looks good.

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[gemini-code-assist]

Code Review

This pull request aims to add support for Qwen3VL dense models by updating the model registries. However, the implementation is incomplete. The new model type QWEN3_VL is missing from MODEL_CONFIG_CONVERTER_REGISTRY, MODEL_INITIALIZER_REGISTRY, and MODEL_WEIGHT_CONVERTER_REGISTRY, which will cause runtime errors. I've added a critical comment to address this. Additionally, it appears the tests have not been updated to cover this new model type, which is crucial for ensuring correctness and preventing future regressions.