extend compute kernel arity to include nullary functions

[jimexist]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

extend compute kernel arity to include nullary functions, so that functions like random() can be implemented without too much overhead

Describe the solution you'd like

Similar to unary, but only takes a usize

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
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