[RNTuple] write multiple fields

[Moelf]

julia> Nitems = 10
       data = [5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
       newtable = Dict(
               "x1" => Float64.(data),
               "x2" => Float32.(data),
               "x3" => Int32.(data),
               "y1" => UInt16.(data),
           )
       UnROOT.write_rntuple(open("/tmp/a.root", "w"), newtable; rntuple_name="myntuple")
       LazyTree("/tmp/a.root", "myntuple")
 Row │ x1       y1      x2       x3
     │ Float64  UInt16  Float32  Int32
─────┼─────────────────────────────────
 1   │ 5.0      5       5.0      5
 2   │ 6.0      6       6.0      6
 3   │ 7.0      7       7.0      7
 4   │ 8.0      8       8.0      8
 5   │ 9.0      9       9.0      9
 6   │ 10.0     10      10.0     10
 7   │ 11.0     11      11.0     11
 8   │ 12.0     12      12.0     12
 9   │ 13.0     13      13.0     13
 10  │ 14.0     14      14.0     14

ROOT is unhappy

[jiling@login04 ~]$ source /cvmfs/sft.cern.ch/lcg/views/dev3/latest/x86_64-el9-gcc11-opt/setup.sh
[jiling@login04 ~]$ python
Python 3.11.9 (main, Jun 24 2024, 14:32:54) [GCC 11.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import ROOT
>>> df =  ROOT.RDataFrame("myntuple", "a.root")
[ROOT.NTuple] Warning /build/jenkins/workspace/lcg_nightly_pipeline/build/projects/ROOT-HEAD/src/ROOT/HEAD/tree/ntuple/v7/src/RPageStorageFile.cxx:326 in ROOT::Experimental::Internal::RPageSourceFile::LoadStructureImpl()::<lambda()>:0: RuntimeWarning: Pre-release format version: RC 2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
cppyy.gbl.ROOT.Experimental.RException: RDataFrame::RDataFrame(string_view treeName, string_view filenameglob, const ROOT::RDataFrame::ColumnNames_t& defaultColumns = {}) =>
    RException: invalid envelope, too short
At:
  static RResult<unsigned int> ROOT::Experimental::Internal::RNTupleSerializer::DeserializeEnvelope(const void*, uint64_t, uint16_t, uint64_t&) [/build/jenkins/workspace/lcg_nightly_pipeline/build/projects/ROOT-HEAD/src/ROOT/HEAD/tree/ntuple/v7/src/RNTupleSerialize.cxx:878]
  static ROOT::Experimental::RResult<void> ROOT::Experimental::Internal::RNTupleSerializer::DeserializeHeader(const void*, uint64_t, ROOT::Experimental::Internal::RNTupleDescriptorBuilder&) [/build/jenkins/workspace/lcg_nightly_pipeline/build/projects/ROOT-HEAD/src/ROOT/HEAD/tree/ntuple/v7/src/RNTupleSerialize.cxx:1649]

• Do round trips within UnROOT.jl
• make ROOT happy

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 43 lines in your changes missing coverage. Please review.

Project coverage is 56.17%. Comparing base (0679f73) to head (a9093ea).

Files with missing lines	Patch %	Lines
src/RNTuple/Writing/TFileWriter.jl	0.00%	41 Missing ⚠️
src/RNTuple/footer.jl	0.00%	2 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (0679f73) and HEAD (a9093ea). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (0679f73)	HEAD (a9093ea)
	3	2

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #349       +/-   ##
===========================================
- Coverage   84.90%   56.17%   -28.73%     
===========================================
  Files          21       21               
  Lines        2994     2971       -23     
===========================================
- Hits         2542     1669      -873     
- Misses        452     1302      +850     

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