ggml: optimize concat op by replacing per-element memcpy with row-level memcpy (#24575)
* ggml: optimize concat op by replacing per-element memcpy with row-level memcpy
* ggml: fix concat offsets for row-level copies
* ggml: add concat row contiguity asserts
* ggml: move concat block size asserts
* ggml: remove redundant concat asserts
* Update ggml/src/ggml-cpu/ops.cpp
Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@huggingface.co>
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Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@huggingface.co>