[Bugfix] Standardize merging multimodal embeddings

[DarkLight1337]

Purpose

Standardize how multimodal embeddings from different modalities are merged in get_multimodal_embeddings:

• Convert to tuple before assigning to the output to handle the case when the embeddings are tensors
• Rename vision_embeddings to image_embeddings to avoid confusing with video_embeddings

FIX #26749

Test Plan

Test Result

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[gemini-code-assist]

Code Review

This pull request standardizes the merging of multimodal embeddings across various models. The changes involve renaming vision_embeddings to image_embeddings for better clarity and ensuring that embeddings are converted to a tuple before being concatenated. This improves code robustness by preventing potential TypeError exceptions when the underlying processing functions return lists instead of tuples. The changes are correct and improve the overall consistency and reliability of the codebase. No issues were found in this pull request.

[BlueBlueFF]

这里没有对image_embeddings的类型和维度校验？ 直接变tuple是否有测试各种情况下的兼容性

[DarkLight1337]

We check ndim inside MultiModalDataParser already. The logic should work for both list of ndim=2 tensors and a single ndim=3 tensor.