Custom properties defined on objects are not accessible from the attribute node when rendering a volume in Cycles. This is because this case is not handled. To handle it, added a primitive type for volumes in the kernel, which is then used in the initialization of ShaderData and to check whether an attribute lookup is for a volume. `volume_attribute_float4` is also now checking the attribute element type to dispatch to the right lookup function. Reviewed By: #cycles, brecht Maniphest Tasks: T87194 Differential Revision: https://developer.blender.org/D11728