Explore argument framework metadata for multiples and alignment

# Explore argument framework metadata for multiples and alignment

We would like to explore extending the `cuda::args` framework with compile-time information beyond static bounds.

One concrete case is representing that a scalar argument is known to be a multiple of a specific value. This could let downstream code specialize without needing the exact constant value.

For sequence arguments, we may also want a way to signal that the referenced memory has a specific alignment. It is not yet clear whether that belongs in the argument framework itself or should be represented by another layer such as pointer/span/mdspan/accessor metadata.

## Questions to answer

- What API should express that a scalar value is a multiple of `N`?
- How should that compose with `static_bounds`, `immediate`, `deferred`, and `constant` arguments?
- What should argument traits expose to consumers?
- Does sequence alignment belong in `cuda::args`, or is there a better abstraction boundary?

This issue tracks the design exploration and any prototype tests needed to decide the direction.