Fix errors when use verl to train GLM4.1v model
Author: kaln27
Pull request: yes
Labels: name: for patch

* Support glm4v load from AutoModelForVision2Seq
* Set glm4v model's _checkpoint_conversion_mapping attribute from None to empty dict {}

# What does this PR do?
When use [verl](https://github.com/volcengine/verl) to train GLM4.1v model with GRPO, there are several small errors.
Here is how to fix them:
- support glm4v load using AutoModelForVision2Seq
- verl treat _checkpoint_conversion_mapping as a dict. But right now is None, which will abort the program. I also found that almost every model which don't need checkpoint convert have a empty dict.

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Comments:
@ArthurZucker 
Hi Arthur, would you mind to review this PR?
Thank your !

Let's address the mapping comment and rebase `main`, before we can merge

**[For maintainers]** Suggested jobs to run (before merge)

run-slow: glm4v

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