[Model] Enable LoRA support for internvl2

[MatteoFari]

Purpose

Enable dynamic LoRA adapters on InternVL2 vision tower + connector (part of #31479) by implementing:

• get_num_mm_encoder_tokens()

• get_num_mm_connector_tokens()

Technical Details

InternVL2 has a CLS token and pixel-shuffle downsampling (downsample_ratio), so LM <IMG_CONTEXT> tokens (post-downsample) don’t match tower tokens (pre-downsample). These helpers map token counts correctly between LM and tower/connector.

Part of #31479.

[github-actions]

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[gemini-code-assist]

Code Review

This pull request enables LoRA support for the InternVL2 model by implementing get_num_mm_encoder_tokens and get_num_mm_connector_tokens. The logic in these new methods is sound. However, I've identified a critical issue that could lead to a ZeroDivisionError and a high-severity maintainability issue due to significant code duplication. I've provided a specific code suggestion to fix the critical bug and a recommendation for refactoring to address the code duplication.

[jeejeelee]

Have you tested this locally?

[MatteoFari]

Hi @jeejeelee, yes I tested it with InternVL2 HF checkpoint (OpenGVLab/InternVL2-1B).
these are the test + logs