Automatic Differentiation

• Concerns: How do we test Ground Truth on GPUs? We can move all data to CPU and use that as GT
• Dump support for Tracker / Reverse Diff -- code will continue to exist. Tests will be dropped to save CI time.
• Zygote goes completely into maintenance mode -- issues resolved on best effort basis. Performance improvements don't need to be ported by default. Community contributions are welcome for these.
• Enzyme / Mooncake have very active maintainers so bugs here are easier to resolve.
• Reactant is the officially recommended solution and will stay as such!

Array Backends

• Drop AMDGPU testing -- code will remain as is. While it has come a long way, I dont reasonably envision supporting AMDGPU.jl given how flaky the tests are. With ROCM support in Reactant nearing, any remaining users of this will be redirected.
• Metal/oneAPI support -- unclear future and anyways these weren't supported by most ops. We are in the process of supporting these via Reactant.
• CUDA support -- remains high priority and testing and performance improvements will be landed.
• For almost all accelerator usecases, Reactant will be the recommended solution!