[Feature] Implement Image Number Limitation for Image Processors

Checklist

• 1. If the issue you raised is not a feature but a question, please raise a discussion at https://github.com/sgl-project/sglang/discussions/new/choose Otherwise, it will be closed.
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Motivation

At present, there is no limitation on the number of images during the processing of mm data. It is necessary to impose such a limitation to prevent potential OOM and other problems.

(When using fast image processor, the GPU memory usage is roughly 1GiB for each 4K image)

Related resources

Implementation Steps:

1. Define a constant, such as IMAGE_NUM_LIMITATION = 5, for each processor.
2. Modify the baseprocessor to utilize this constant for request validation.
3. Incorporate a server argument to enable modification of this numerical value.

In case you lack familiarity with the mm data processing pipeline, it is advisable to first refer to here