Allow benchmark_differentiation to (also) record the mean time

[nsiccha]

Currently (I think) DifferentiationInterfaceTest.benchmark_differentiation only records the minimum benchmark runtime (see

DifferentiationInterface.jl/DifferentiationInterfaceTest/src/tests/benchmark.jl

Line 104 in 1e012dc

time=bench_min.time,

), but it would also be nice to be able to choose the mean benchmark runtime.

[gdalle]

That's a good idea! I think the best way is to add a keyword argument like "benchmark_aggregation" which defaults to the min function, and use it when aggregating samples.

[gdalle]

@nsiccha I think #639 gives you the flexibility you need

[nsiccha]

Cool!