metal: optimise `GGML_OP_SUM` (#16559)
* optimise GGML_OP_SUM
* add non-contiguous tests by permuting the input
* change tests to require full contiguity of OP_SUM
* cuda : add check GGML_OP_SUM
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Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>
