[ntuple] Support storage of a SOA using contiguous memory

[jblomer]

Feature description

This topic was originally brought up for TTree as https://its.cern.ch/jira/browse/ROOT-9626

Meanwhile, the topic continued to be discussed in the context of RNTuple. The latest state is summarized in the RNTuple 2024 workshop:
https://indico.cern.ch/event/1468611/contributions/6223333/attachments/2979013/5244951/20241203_Hahnfeld_SoA.pdf

It is an ongoing R&D item in 2025

Alternatives considered

No response

Additional context

No response