#shlo_ref Rework quantized tensor element types.
#shlo_ref Rework quantized tensor element types.

This separates the implementation of per-tensor and per-axis quantization
types. The goal is to allow value parametrized tests without having to use
templating mechanisms to create the values. This will also make the user
dispatching code much more concise.

- Information duplication is reduced in the quantized type structures (only the variants).
- The code is better decoupled.
- Per-tensor does not need to get the per axis 0th element for scales and zero points.
