66def34e0e
At present, if a VFS is used but an OBJ or PNG asset doesn't exist in the VFS, the model compilation will fail without trying to first locate the asset on disk. This breaks the Python bindings `MjModel.from_xml_string` almost entirely when OBJ assets are involved. Also modify error messages to disambiguate between different modes of asset loading failures. PiperOrigin-RevId: 526637686 Change-Id: Iba02cc94989083bc2835a3e67dfc78c0a21047e9