copy instead of reintertrept() for leaf columns

[Moelf]

fix #278

From 143s down to 6.4s :

Test Summary:        | Pass  Total  Time
RNTuple multicluster |    5      5  6.4s

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Files	Coverage Δ
src/RNTuple/fieldcolumn_reading.jl	93.51% <100.00%> (-0.24%)	⬇️
src/RNTuple/footer.jl	96.96% <100.00%> (ø)

📢 Thoughts on this report? Let us know!.

[Moelf]

this is weird:

Setup

using UnROOT
const f1 = UnROOT.samplefile("RNTuple/test_ntuple_int_multicluster.root")

function main()
    df = LazyTree(f1, "ntuple")
    unique(df.one_integers[1:end÷2]) == [2]
    unique(df.one_integers[end÷2+1:end]) == [1]
    df.one_integers[1] == 2
    df.one_integers[end] == 1
    length(df.one_integers) == 50000000 * 2
end

1.10

julia> @time df.one_integers[1];
  0.841748 seconds (582.83 k allocations: 419.404 MiB, 2.23% gc time, 84.14% compilation time)

julia> @time df.one_integers[end];
  0.146485 seconds (18.34 k allocations: 383.358 MiB, 15.27% gc time)

julia> @time main();
  3.735243 seconds (214.63 k allocations: 1.693 GiB, 6.12% gc time, 2.69% compilation time)

1.9

julia> @time df.one_integers[1];
  4.564458 seconds (100.66 M allocations: 1.906 GiB, 2.01% gc time, 16.69% compilation time)

julia> @time df.one_integers[end];
  3.774830 seconds (100.02 M allocations: 1.864 GiB, 2.86% gc time)

julia> @time main();
 18.655775 seconds (400.26 M allocations: 7.656 GiB, 2.59% gc time, 0.62% compilation time)

[Moelf]

# before
julia> @time main(df)
 19.891766 seconds (600.07 M allocations: 13.605 GiB, 5.07% gc time)
true

# after
julia> @time main(df)
  3.216152 seconds (73.35 k allocations: 1.684 GiB)
true

ugh, we really need to integrate some kind of Cthulu testing