ALab does not render with PRMan

[chrizzFTD]

Currently, the ALab fails to render out of the box with RenderMan-25 and 26.

Having tested in Windows and Houdini-19, with RenderMan-25:

Some reasons identified for this to not work:

• Relative UDIM paths as provided
• Relative UDIM paths with <udim> instead of <UDIM>
• Absolute UDIM paths with <udim> instead of <UDIM> and .exr
• Transparency on the materials (see glasses and page holes)

What does work (only in 25.0 not in 25.1):

• In RIS: Absolute UDIM paths with <udim> instead of <UDIM>
• In both (RIS and XPU): Absolute UDIM paths with <udim> instead of <UDIM> and .tx instead of .exr
• Changing the builtin Primvar reader node with a custom one from PRMan

With these changes, the result is:

It would be good to run the tests again in PRMan-26, with a branch that provides changes to "work around" for a successful render and include the Pixar team in the conversation.