Optimize axis-independent reduction functions for OffsetRanges

[jishnub]

Currently

julia> @btime sum(a) setup = (a = OffsetVector(1:rand(10000:10000),3));
  3.851 μs (0 allocations: 0 bytes)

julia> @btime sum(a.parent) setup = (a = OffsetVector(1:rand(10000:10000),3));
  4.262 ns (0 allocations: 0 bytes)

Is there a way to use the fact that the parent is an AbstractRange and avoid iterating over it?

[timholy]

Presumably if you create it as an IdOffsetRange rather than an OffsetVector?

[timholy]

But of course you could add a specialization for reductions.