Refactor add_item to infer kernel inputs from the graph instead of explicitly adding them.

[cianciosa]

Currently framework users must explicitly pass the input variables and random state needed by a kernel. This could be inferred from the graph it self. It is currently not performed this way because historical reasons. compile_preamble methods could be refactored to collect unique input nodes needed. These can be fed to the create_kernel_prefix in the gpu backends to build the kernel argument signatures.