Add some EnzymeRules

[MasonProtter]

Currently, Enzyme.jl's reverse mode autodiff doesn't work correctly with Bumper.jl because if you give it a Duplicated buffer, it'll += accumulate results into the duplicated buffer making the answer depend on the state of the buffer at the start of the program.

It'd be good if we could set up some EnzymeRules to explicitly teach Enzyme how to handle Bumper.jl allocations and deallocations. I don't really know how to do this though, so if anyone wants to take it on, or work on it together please do.

[MilesCranmer]

Just so I understand, you could still use bump allocation internal to a differentiated function, right? You are basically wondering if it could also be done with bump allocation wrapping an enzyme call?

[MasonProtter]

I'm pretty sure it'll not work even if you do it internally (unless you manually zero out your buffer)

[sefffal]

I checked, and yes Enzyme fails to autodiff a function that uses Bumper internally, so I think rules are needed.