fix(config): add deepstack_visual_indexes to Qwen3_5MoeVisionConfig

[hijingsong]

Problem

The @strict decorator on Qwen3_5MoeVisionConfig silently drops the deepstack_visual_indexes field during config loading because it is not declared as a class attribute. Every Qwen3.5 MoE model on HuggingFace ships with this field in its config.json (e.g. Qwen/Qwen3.5-35B-A3B-Base).

Root Cause

Qwen3_5MoeVisionConfig inherits from Qwen3_5VisionConfig, which overrides deepstack_visual_indexes with an AttributeError() sentinel (inherited from the parent chain). The generated configuration_qwen3_5_moe.py does not include the field at all, so @strict rejects it when deserializing from config.json.

Fix

Override deepstack_visual_indexes as a properly typed class attribute on Qwen3_5MoeVisionConfig with default (), matching the type annotation used in Qwen3VLVisionConfig. This ensures:

• The field is accepted when loading model configs
• config.vision_config.deepstack_visual_indexes returns the value from config.json
• No silent data loss during deserialization

Verification

from transformers import AutoConfig
config = AutoConfig.from_pretrained("Qwen/Qwen3.5-35B-A3B-Base", trust_remote_code=True)
print(config.vision_config.deepstack_visual_indexes)  # [] — no longer raises AttributeError

Fixes #45375

Changes

• modular_qwen3_5_moe.py: Add deepstack_visual_indexes field override with docstring
• configuration_qwen3_5_moe.py: Add deepstack_visual_indexes field with docstring (generated)

[github-actions]

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

run-slow: qwen3_5_moe

[Rocketknight1]

cc @zucchini-nlp, more stuff related to #41250!

[zucchini-nlp]

@hijingsong see the comment under issue, not reproducible for me so I am guessing something is different env-setup