kleidiai: add optimized per-channel kernels for Q8_0

[chaxu01]

Benchmarks from MacBook M4:

W/ KleidiAI

GGML_KLEIDIAI_SME=1 ./bin/llama-bench -m ./Llama-3.2-1B-Instruct-Q8_0.gguf -ngl 0 -t 1
| model                          |       size |     params | backend    | threads |            test |                  t/s |
| ------------------------------ | ---------: | ---------: | ---------- | ------: | --------------: | -------------------: |
| llama 1B Q8_0                  |   1.22 GiB |     1.24 B | CPU        |       1 |           pp512 |        504.01 ± 2.70 |
| llama 1B Q8_0                  |   1.22 GiB |     1.24 B | CPU        |       1 |           tg128 |         93.68 ± 0.16 |

GGML_KLEIDIAI_SME=0 ./bin/llama-bench -m ./Llama-3.2-1B-Instruct-Q8_0.gguf -ngl 0 -t 1,4
| model                          |       size |     params | backend    | threads |            test |                  t/s |
| ------------------------------ | ---------: | ---------: | ---------- | ------: | --------------: | -------------------: |
| llama 1B Q8_0                  |   1.22 GiB |     1.24 B | CPU        |       1 |           pp512 |        193.94 ± 1.22 |
| llama 1B Q8_0                  |   1.22 GiB |     1.24 B | CPU        |       1 |           tg128 |         43.45 ± 0.34 |
| llama 1B Q8_0                  |   1.22 GiB |     1.24 B | CPU        |       4 |           pp512 |        692.11 ± 0.71 |
| llama 1B Q8_0                  |   1.22 GiB |     1.24 B | CPU        |       4 |           tg128 |       132.24 ± 16.44 |

W/O KleidiAI

./bin/llama-bench -m ./Llama-3.2-1B-Instruct-Q8_0.gguf -ngl 0 -t 1,4
| model                          |       size |     params | backend    | threads |            test |                  t/s |
| ------------------------------ | ---------: | ---------: | ---------- | ------: | --------------: | -------------------: |
| llama 1B Q8_0                  |   1.22 GiB |     1.24 B | CPU        |       1 |           pp512 |         44.39 ± 0.52 |
| llama 1B Q8_0                  |   1.22 GiB |     1.24 B | CPU        |       1 |           tg128 |         41.61 ± 0.25 |
| llama 1B Q8_0                  |   1.22 GiB |     1.24 B | CPU        |       4 |           pp512 |        156.83 ± 0.62 |
| llama 1B Q8_0                  |   1.22 GiB |     1.24 B | CPU        |       4 |           tg128 |        115.41 ± 1.82 |

[chaxu01]

Hi @ggerganov, this PR adds Q8_0 optimization kernels for the KleidiAI backend.
The CI shows three failed cases, but they appear to be unrelated (KleidiAI isn’t enabled in those jobs).
Please take a look when you have a moment, thanks!

[ggerganov]

@chaxu01 Shall we first merge the CI runner (#17021) and then this PR?