Add Q4_3 quantization (ARM NEON)

[ggerganov]

Initial Q4_3 implementation runs at ~82 ms / token on M1.
Need to see if we can optimize that somehow.

For example Q4_1 runs at ~55 ms / token, so there is probably lots of room for improvement

#define QK4_3 16
typedef struct {
    ggml_fp16_t d;         // delta
    ggml_fp16_t m;         // min
    uint8_t qs[QK4_3 / 2]; // nibbles / quants
} block_q4_3;

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Merging this, although the speed is not satisfying. We have to try to get it as fast as Q4_1.
We might have to change the block_q4_3 if needed to achieve this

[prusnak]

M1 16 GB benchmark:

7B q4_3 4 threads: 180 ms/token
7B q4_3 8 threads: 280 ms/token