Bump to transformers v5 and fix ColPali processor compatibility

[ManuelFay]

• Add regression tests for ColPaliProcessor to validate Transformers v5 modality registration and fallback loading behavior when a processor bundle is incomplete.

Changed

• Bump runtime compatibility to transformers>=5.0.0,<6.0.0, peft>=0.18.0,<0.19.0, and accelerate>=1.1.0,<2.0.0.
• Update supported Python versions to >=3.10,<3.15 and align CI workflows to Python 3.10–3.14.
• Update all affected processor subclasses (Qwen2/Qwen2.5/Qwen3, Gemma3, Idefics3, ModernVBert, Qwen2.5 Omni) to explicit __init__ modality signatures required by Transformers v5 ProcessorMixin.

Fixed

• Fix ColPali/PaliGemma model loading under Transformers v5 by adapting wrapper internals to new module layout and tied-weights expectations.
• Fix ColPali processor loading for checkpoints without a complete processor bundle by explicitly falling back to AutoImageProcessor + AutoTokenizer.
• Fix ColPali collator image token id lookup to use convert_tokens_to_ids, compatible with Transformers v5 tokenizer backend changes.
• Fix test collection on Python 3.14 by making tests an explicit package (tests/__init__.py).
• Fix CI formatting failure by applying ruff format to updated ColPali processing tests.
• Fix ColQwen2 and ColQwen2.5 initialization across Transformers versions by resolving hidden size from either config.hidden_size or config.text_config.hidden_size.
• Call post_init() in ColIdefics3 and ColModernVBert to align model initialization with Transformers v5 expectations.
• Improve VisualRetrieverCollator image token id resolution by preferring processor-level image_token_id when available.
• Fix ColQwen2 and ColQwen2.5 LoRA checkpoint key remapping for custom_text_proj (base_model.model.* -> model keys) to avoid missing/unexpected adapter keys at load time.
• Fix ColPali LoRA adapter key remapping for custom_text_proj (base_model.model.* -> model keys) and ignore expected missing model.lm_head.weight during load.
• Fix ColModernVBert LoRA adapter key remapping for custom_text_proj (base_model.model.* -> model keys) to avoid missing/unexpected adapter keys at load time.

[ManuelFay]

• I tested end to end on colpali, colqwené, colqwen2.5, colmodernvbert, colqwenomni;

not tested colqwen3 and colgemma because no model weights are public - which is annoying

[ManuelFay]

Note: The slow tests show some regressions on ColPali - not exactly the same behavior.
Running the slow tests with the old package version shows this was already the case - and that the values are very similar with before this PR. If there was a regression, it happened before so should be mergeable !