Adding ability to have meta data per tensor row

[ikawrakow]

ggml is very opinionated on the topic of tensor data layout - things must be organized in blocks of a known size, the number of elements in a block must be fixed, etc. There are many places where it is assumed that a contiguous tensor row with ne elements occupies ne * ts / bs bytes, where ts is the "type size" and bs is the "block size". This is not very useful when one wants to have some meta data per tensor or per row (e.g., tensor or row scale, quant values in a K-means clustering based quantization, etc.).

This PR adds the ability to have per row meta data. As a POC, IQ1_TN and IQ2_TN are changed to have a row-wise block scale, which reduces the quantized model size to 1.625 (IQ1_TN) or 2.0 (IQ2_TN) bpw from 1.6875 or 2.0625 bpw.

There are a few places left in the CUDA Flash Attention implementation where the ne * ts / bs assumption is used. But as we are not using quants with row meta data for quantized KV cache, this should be OK for now.

This is a breaking change. Previously created IQ1_TN and IQ2_TN models need to be re-quantized.