[EvoArt]

Add AutoPiste for Piste.jl, a forward- and reverse-mode AD package whose derivatives survive juliac --trim. A DifferentiationInterface extension for it is in JuliaDiff/DifferentiationInterface.jl#1089 (draft until this is released).

AutoPiste()                                # forward mode, dual numbers
AutoPiste(; chunksize = 8)                 # forward mode, fixed chunk width
AutoPiste(; mode = ADTypes.ReverseMode())  # reverse mode, a tape

Design

• One struct, with ADTypes' own mode objects as the mode field. Piste has both modes in one package, so I followed AutoEnzyme (mode as a field) rather than AutoMooncake/AutoMooncakeForward, which I understand were split only to avoid a breaking release. mode(::AutoPiste) returns the field, and the type parameter is restricted to Union{ForwardMode, ReverseMode}.
• chunksize is a type parameter, as for AutoForwardDiff. This matters more than usual for Piste: under --trim the chunk width has to be known statically, so trimmed code passes an explicit value.
• Default mode is forward.

Open questions, happy to change either:

1. ForwardMode/ReverseMode are public but not exported, so users write ADTypes.ReverseMode(). Would you prefer symbols (mode = :reverse), or two structs?
2. Forward or reverse as the default?

Changes

AutoPiste struct, docstring, mode, show, export, Auto(:Piste), the docs page, and tests in test/dense.jl, test/misc.jl and test/symbols.jl.

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