metal : reorder write loop in mul mat kernel + style

[ggerganov]

Minor optimization for BS>1 by writing the results using float4 instead of float.

./scripts/compare-commits.sh master gg/metal-mul-mat-write-opt -m ./models/llama-3.2-3b-instruct/ggml-model-q4_0.gguf -m ./models/llama-3.1-8b/ggml-model-q4_k.gguf -m models/llama-3.2-1b-instruct/ggml-model-q8_0.gguf -m models/qwen2.5-7b-coder/ggml-model-q8_0.gguf -m models/qwen2.5-1.5b-coder/ggml-model-f16.gguf -fa 1 -p 511,512,1,2,3,4,5,6,7,8 -n 128

CPU	Model	Test	t/s master	t/s gg/metal-mul-mat-write-opt	Speedup
M2 Ultra	llama 1B Q8_0	pp1	232.67	230.65	0.99
M2 Ultra	llama 1B Q8_0	pp2	125.45	133.59	1.06
M2 Ultra	llama 1B Q8_0	pp3	188.18	198.16	1.05
M2 Ultra	llama 1B Q8_0	pp4	250.57	265.69	1.06
M2 Ultra	llama 1B Q8_0	pp5	313.60	331.30	1.06
M2 Ultra	llama 1B Q8_0	pp6	376.26	397.60	1.06
M2 Ultra	llama 1B Q8_0	pp7	434.15	460.83	1.06
M2 Ultra	llama 1B Q8_0	pp8	496.23	531.32	1.07
M2 Ultra	llama 1B Q8_0	pp511	7650.92	7744.50	1.01
M2 Ultra	llama 1B Q8_0	pp512	7791.42	7801.47	1.00
M2 Ultra	llama 1B Q8_0	tg128	230.77	231.00	1.00
M2 Ultra	llama 3B Q4_0	pp1	155.76	155.40	1.00
M2 Ultra	llama 3B Q4_0	pp2	61.35	64.07	1.04
M2 Ultra	llama 3B Q4_0	pp3	91.48	95.32	1.04
M2 Ultra	llama 3B Q4_0	pp4	118.39	124.69	1.05
M2 Ultra	llama 3B Q4_0	pp5	147.37	155.11	1.05
M2 Ultra	llama 3B Q4_0	pp6	177.50	185.52	1.05
M2 Ultra	llama 3B Q4_0	pp7	205.60	215.63	1.05
M2 Ultra	llama 3B Q4_0	pp8	234.92	247.89	1.06
M2 Ultra	llama 3B Q4_0	pp511	2863.44	2962.87	1.03
M2 Ultra	llama 3B Q4_0	pp512	2908.56	2988.59	1.03
M2 Ultra	llama 3B Q4_0	tg128	155.74	155.60	1.00
M2 Ultra	llama 8B Q4_K_M	pp1	85.79	85.90	1.00
M2 Ultra	llama 8B Q4_K_M	pp2	28.87	29.79	1.03
M2 Ultra	llama 8B Q4_K_M	pp3	43.22	44.40	1.03
M2 Ultra	llama 8B Q4_K_M	pp4	56.79	58.38	1.03
M2 Ultra	llama 8B Q4_K_M	pp5	71.16	72.81	1.02
M2 Ultra	llama 8B Q4_K_M	pp6	85.22	87.56	1.03
M2 Ultra	llama 8B Q4_K_M	pp7	98.90	101.67	1.03
M2 Ultra	llama 8B Q4_K_M	pp8	113.33	116.40	1.03
M2 Ultra	llama 8B Q4_K_M	pp511	1114.44	1118.62	1.00
M2 Ultra	llama 8B Q4_K_M	pp512	1128.36	1124.39	1.00
M2 Ultra	llama 8B Q4_K_M	tg128	85.86	85.52	1.00
M2 Ultra	qwen2 1.5B F16	pp1	112.38	112.68	1.00
M2 Ultra	qwen2 1.5B F16	pp2	81.90	88.56	1.08
M2 Ultra	qwen2 1.5B F16	pp3	122.75	130.37	1.06
M2 Ultra	qwen2 1.5B F16	pp4	158.62	169.50	1.07
M2 Ultra	qwen2 1.5B F16	pp5	197.93	212.72	1.07
M2 Ultra	qwen2 1.5B F16	pp6	241.20	255.49	1.06
M2 Ultra	qwen2 1.5B F16	pp7	280.54	298.75	1.06
M2 Ultra	qwen2 1.5B F16	pp8	321.05	336.54	1.05
M2 Ultra	qwen2 1.5B F16	pp511	6035.39	6208.76	1.03
M2 Ultra	qwen2 1.5B F16	pp512	6251.98	6257.90	1.00
M2 Ultra	qwen2 1.5B F16	tg128	110.76	110.69	1.00
M2 Ultra	qwen2 7B Q8_0	pp1	67.37	68.35	1.01
M2 Ultra	qwen2 7B Q8_0	pp2	35.29	36.57	1.04
M2 Ultra	qwen2 7B Q8_0	pp3	53.36	54.62	1.02
M2 Ultra	qwen2 7B Q8_0	pp4	69.73	71.91	1.03
M2 Ultra	qwen2 7B Q8_0	pp5	86.87	89.66	1.03
M2 Ultra	qwen2 7B Q8_0	pp6	104.37	107.63	1.03
M2 Ultra	qwen2 7B Q8_0	pp7	121.80	125.39	1.03
M2 Ultra	qwen2 7B Q8_0	pp8	139.49	143.51	1.03
M2 Ultra	qwen2 7B Q8_0	pp511	1347.18	1355.80	1.01
M2 Ultra	qwen2 7B Q8_0	pp512	1358.74	1360.51	1.00
M2 Ultra	qwen2 7B Q8_0	tg128	67.48	67.62	1.00