ggml : make i-quants work with super-blocks of 64 (CPU,Metal) (llama/5760)

ggml : make i-quants work with super-blocks of 64 (CPU,Metal) (llama/5760)

* WIP: make i-quants work for QK_K = 64

* iq2_xs: attempt to fix AVX dot product for QK_K = 64

Tests pass, but I get gibberish.

* QK_K = 64 tests pass on ARM_NEON and Metal

Sadly, that does not mean it actually works.

* Make CUDA compile with QK_K = 64

Tests don't pass, plus we get misaligned access

* Q2_K: fixed bug in imatrix quantization for QK_K = 64

* iq1_s: turn off SIMD implementation for QK_K = 64 (it does not work)

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Co-authored-by: Iwan Kawrakow <redacted>