[Utilities] use foldl to avoid StackOverflow

[blegat]

Alternative fix to #2285

The for loop is quite weird as you expect the list of arguments to be a tuple of mixed argument types.
I think there is a win of not doing the recursion and falling back to a for loop at some point but I think it's at least more readable to use the standard afold for this.

This shows a big win on @odow's benchmark in #2284 (comment)

julia> import MathOptInterface as MOI

julia> using BenchmarkTools

julia> function my_operate(::typeof(+), ::Type{T}, f, g, h, args...) where {T<:Number}
           ret = MOI.Utilities.operate(+, T, f, g)
           ret = MOI.Utilities.operate!(+, T, ret, h)
           for a in args
               ret = MOI.Utilities.operate!(+, T, ret, a)
           end
           return ret
       end
my_operate (generic function with 1 method)

julia> f = (
           MOI.VariableIndex(1),
           1 * MOI.VariableIndex(1) + 2,
           3 * MOI.VariableIndex(1) * MOI.VariableIndex(1) + 4,
       )
(MOI.VariableIndex(1), (2) + (1) MOI.VariableIndex(1), (4) + 3.0 MOI.VariableIndex(1)²)

julia> x = f[[2, 1, 2, 1, 2, 3]]
((2) + (1) MOI.VariableIndex(1), MOI.VariableIndex(1), (2) + (1) MOI.VariableIndex(1), MOI.VariableIndex(1), (2) + (1) MOI.VariableIndex(1), (4) + 3.0 MOI.VariableIndex(1)²)

julia> foo(x) = MOI.Utilities.operate(+, Int, x...)
foo (generic function with 1 method)

julia> bar(x) = my_operate(+, Int, x...)
bar (generic function with 1 method)

julia> @benchmark foo($x)
BenchmarkTools.Trial: 10000 samples with 996 evaluations.
 Range (min … max):  25.117 ns …  1.026 μs  ┊ GC (min … max):  0.00% … 95.46%
 Time  (median):     28.674 ns              ┊ GC (median):     0.00%
 Time  (mean ± σ):   35.176 ns ± 56.915 ns  ┊ GC (mean ± σ):  10.90% ±  6.54%

  ▁ ▆█▇▅▅▅▃▂▂▁▁▁                                              ▂
  █▇█████████████████████▇▇▇▆▇▆▆▆▅▇▇▇█▅▄▆▇▇▅▅▅▄▄▅▄▄▄▃▃▄▄▆▇▆▇█ █
  25.1 ns      Histogram: log(frequency) by time      74.8 ns <

 Memory estimate: 224 bytes, allocs estimate: 2.

julia> @benchmark bar($x)
BenchmarkTools.Trial: 10000 samples with 206 evaluations.
 Range (min … max):  379.612 ns …  11.897 μs  ┊ GC (min … max): 0.00% … 95.58%
 Time  (median):     419.449 ns               ┊ GC (median):    0.00%
 Time  (mean ± σ):   466.205 ns ± 502.626 ns  ┊ GC (mean ± σ):  5.41% ±  4.83%

     ▃▄▆▇▇█▆▅▄▄▃▂▂▂▁   ▁▁▁▁ ▁▁▁▁▂▁▁▁▁▁                          ▂
  ▇▇███████████████████████████████████▇█▇█▇▇▆▇▆▆▆▇▇▆▇████▇▇▆▅▆ █
  380 ns        Histogram: log(frequency) by time        673 ns <

 Memory estimate: 608 bytes, allocs estimate: 9.

[odow]

I don't think your benchmark is correct because there was a bug in your method. The 25.117 ns is too small to be realistic.

Here's what I get now:

julia> import MathOptInterface as MOI

julia> using BenchmarkTools

julia> function my_operate(::typeof(+), ::Type{T}, f, g, h, args...) where {T<:Number}
           ret = MOI.Utilities.operate(+, T, f, g)
           ret = MOI.Utilities.operate!(+, T, ret, h)
           for a in args
               ret = MOI.Utilities.operate!(+, T, ret, a)
           end
           return ret
       end
my_operate (generic function with 1 method)

julia> f = (
           MOI.VariableIndex(1),
           1 * MOI.VariableIndex(1) + 2,
           3 * MOI.VariableIndex(1) * MOI.VariableIndex(1) + 4,
       )
(MOI.VariableIndex(1), (2) + (1) MOI.VariableIndex(1), (4) + 3.0 MOI.VariableIndex(1)²)

julia> x = f[[2, 1, 2, 1, 2, 3]]
((2) + (1) MOI.VariableIndex(1), MOI.VariableIndex(1), (2) + (1) MOI.VariableIndex(1), MOI.VariableIndex(1), (2) + (1) MOI.VariableIndex(1), (4) + 3.0 MOI.VariableIndex(1)²)

julia> foo(x) = MOI.Utilities.operate(+, Int, x...)
foo (generic function with 1 method)

julia> bar(x) = my_operate(+, Int, x...)
bar (generic function with 1 method)

julia> @benchmark foo($x)
BenchmarkTools.Trial: 10000 samples with 641 evaluations.
 Range (min … max):  191.588 ns …   6.407 μs  ┊ GC (min … max):  0.00% … 96.14%
 Time  (median):     207.365 ns               ┊ GC (median):     0.00%
 Time  (mean ± σ):   251.995 ns ± 436.067 ns  ┊ GC (mean ± σ):  14.51% ±  8.04%

  ▇▆▆█▅▂▁ ▁   ▁▁▁▁                                              ▁
  ████████████████▇▇█▇█▇▇█▇▆▇▆▅▅▅▆▆▆▆▅▆▆▄▅▅▄▅▆▄▅▅▃▄▄▄▄▄▅▄▅▃▄▄▄▄ █
  192 ns        Histogram: log(frequency) by time        491 ns <

 Memory estimate: 576 bytes, allocs estimate: 7.

julia> @benchmark bar($x)
BenchmarkTools.Trial: 10000 samples with 155 evaluations.
 Range (min … max):  669.084 ns …  25.458 μs  ┊ GC (min … max): 0.00% … 96.29%
 Time  (median):     697.110 ns               ┊ GC (median):    0.00%
 Time  (mean ± σ):   774.301 ns ± 948.249 ns  ┊ GC (mean ± σ):  5.08% ±  4.06%

  ▄█▇▅▃▁          ▁                                             ▁
  ██████▆▇███▆▇▅▇▇███▇▆▅▆▅▆▆▅▄▆▅▅▆▇▆▅▅▅▅▅▅▅▃▄▄▄▄▄▆▄▄▄▄▄▅▄▄▄▅▅▅▄ █
  669 ns        Histogram: log(frequency) by time       1.56 μs <

 Memory estimate: 608 bytes, allocs estimate: 9.