Much faster prompt processing for IQK quants (ARM_NEON)

[ikawrakow]

It is time to give some attention to the ARM_NEON back-end, which has fallen behind quite a bit.

This PR corresponds to PRs #531, #533, #534, #546 and applies the on-the-fly repacking technique to IQK quants (IQ2_KS, IQ2_K, IQ3_K, IQ4_KS, IQ4_K, IQ5_KS, IQ5_K, IQ6_K) for the ARM_NEON implementation.

Here is a PP-512 performance comparison between the main branch and this PR for LlaMA-3.1-8B-Instruct on M2-Max

type	t/s (main)	t/s (PR)	Speedup
IQ2_KS	75.66	166.10	2.195
IQ2_K	47.40	166.94	3.522
IQ3_K	47.28	166.48	3.521
IQ4_KS	70.03	167.32	2.389
IQ4_K	46.41	167.19	3.602
IQ5_KS	63.76	166.01	2.604
IQ5_K	45.80	167.57	3.569
IQ6_K	43.92	164.29	3.741

At this point IQK quants are the top tier quants for prompt processing speed on ARM_NEON.