[Libre-soc-dev] SimdSignal update

[lkcl]

https://libre-soc.org/3d_gpu/architecture/dynamic_simd/shape/

underway.  section "SimdShape arithmetic"

those three examples covers the immediate needs, which can be expanded on-demand.  three cases are shown:

* rudimentary integer arithmetic (shape * 2)
* fixed width to fixed width (shape + shape)
* fixed width to elwidths (shape + shape)

this last one is the odd one where elwidths have to take priority even though one shape is fixed width, it sorta intuitively makes sense that elwidths have to take priority.

i will add some text about this now.

l.