* model : refactor QKV into common build_qkv and create_tensor_qkv helpers
* model : extend build_qkv to bert/mpt/dbrx/olmo/lfm2/nemotron-h/granite-hybrid/gemma3n-iswa/t5-dec and fix wqkv_s
* Add control vector functions to qwen3.5 and qwen-next models
* Add missing cvec compatibility to the rest of the models
* Adjust comments and formatting
* cleanup
* whitespace
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Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>