Lots of allocations when writing DateTimes

[akosuas]

I was having some crazy GC pauses, and tracked it down to this:

using Dates
using Arrow

julia> tstamps = DateTime.(zeros(1_000_000));
julia> @time Arrow.write("test.arrow", (;t=tstamps))
  0.055171 seconds (1.00 M allocations: 24.274 MiB)
"test.arrow"

There seems to be one allocation per DateTime. I'm on julia 1.6.1, Arrow 1.4.1.

Thanks!