feat(vello_hybrid): Add clipping support for image rendering

[grebmeg]

This PR adds clipping support for image rendering in vello_hybrid, allowing images to be correctly clipped by multiple nested clip layers.

The x, y coordinates used for sampling depend on clip depth. If a strip is not in clipped space, it receives global strip view coordinates. Otherwise, it uses local slot coordinates, which results in incorrect image sampling — since sampling must occur relative to the global strip position. To address this, position data is now passed for all strips associated with image paints.

Additionally, the logic for determining whether to sample color from a solid rgba value, an image texture, or a slot texture has been refined. The flag used for this distinction was reduced from an 8-bit field to a 1-bit discriminator, enabling the rgba_or_slot field to be reused as a payload across different paint modes.