[VLM] Optimize GLM4.5-V-style video processing to only decode necessary frames

[Isotr0py]

Purpose

• To make sure video processing correctness for GLM4.5V and upcoming Qwen3-VL, we need to add --media-io-kwargs '{"video": {"num_frames": -1}}', which is not safe enough and cause extremly high RAM usage to crash server if input video is quite long.
• This PR adds a new video loader to support GLM4.5V-style dynamic sampling, so we don't need to decode all frames anymore.

Test Plan

Test Result

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[Isotr0py]

Benchmark results

Script: https://gist.github.com/Isotr0py/921b17edaeef1ed8bc211e22b47c84b4
Hardware: AMD Ryzen Threadripper 3970X 32-Core Processor

[Full decoding backend processing] start
[Full decoding backend processing] memory cost: 4396.312MB
[Full decoding backend processing] time cost: 27.156s

[Dynamic decoding backend processing] start
[Dynamic decoding backend processing] memory cost: 500.066MB
[Dynamic decoding backend processing] time cost: 12.666s

[DarkLight1337]

Is there a link to the relevant issue so we know when to remove this workaround?

[Isotr0py]

The root issue is the hardcoded 24 fps in Transformers v4.55's no sampling code path:
https://github.com/huggingface/transformers/blob/d79b2d981f28b2730d402244ac3c2e9a8c054eee/src/transformers/models/glm4v/video_processing_glm4v.py#L173-L176

I think huggingface/transformers#39600 should have fixed this issue. And we can remove this after Transformers v4.56 update. (Although current GLM4.1V's vLLM multimodal processor is broken on Transformers v4.56, I would like to fix it in following PR together 😅)