This commit adds infrastructure for 8 bit signed integer attributes.
This can be useful given the discussion in T94193, where we want to
store spline type, Bezier handle type, and other small enums as
attributes.

This is only exposed in the interface in the attribute lists, so it
shouldn't be an option in geometry nodes, at least for now.
I expect that this type won't be used directly very often, it
should mostly be cast to an enum type. However, with support
for 8 bit integers, it also makes sense to add things like mixing
implementations for consistency.