Making an iterator that splats keys and values quickly into kwargs

[uniment]

@flipgthb

If you want an iterator for MyStruct, here is a suggestion

Now both splatting approaches are slow, ha.

@btime let; [(; MyStruct((a=rand(),b=rand()),(c=rand(),d=rand()))...) for i=1:1000] end;
#    1.781 ms (58004 allocations: 2.76 MiB)
@btime let; [(MyStruct((a=rand(),b=rand()),(c=rand(),d=rand()))...,) for i=1:1000] end;
#    816.800 μs (34010 allocations: 1.60 MiB)