Q6_K AVX improvements (llama/10118)

Q6_K AVX improvements (llama/10118)

* q6_k instruction reordering attempt

* better subtract method

* should be theoretically faster

small improvement with shuffle lut, likely because all loads are already done at that stage

* optimize bit fiddling

* handle -32 offset separately. bsums exists for a reason!

* use shift

* Update ggml-quants.c

* have to update ci macos version to 13 as 12 doesnt work now. 13 is still x86