[ntuple] add read support to SoA I/O

[jblomer]

Tutorial output:

************************************ NTUPLE ************************************
* N-Tuple : ntpl                                                               *
* Entries : 4                                                                  *
********************************************************************************
* Field 1           : points (PointSoA)                                        *
*   Field 1.1       : _0 (PointRecord)                                         *
*     Field 1.1.1   : fX (float)                                               *
*     Field 1.1.2   : fY (float)                                               *
********************************************************************************
Approximated PI with 100 points to 3.2
Approximated PI with 500 points to 3.104
Approximated PI with 1000 points to 3.172
Approximated PI with 10000 points to 3.1388

[github-actions]

Test Results

    22 files      22 suites   3d 7h 34m 9s ⏱️
 3 851 tests  3 849 ✅ 0 💤 2 ❌
76 051 runs  76 048 ✅ 0 💤 3 ❌

For more details on these failures, see this check.

Results for commit c41fbb0.

♻️ This comment has been updated with latest results.