[ntuple][python][ATLAS experiment] Re-Implement context management pr…

[rybkine]

…otocol for RNTupleReader/Writer

bindings/pyroot/pythonizations/python/ROOT/_pythonization/_rntuple.py: add __enter__ method - returns self (an instance of RNTupleReader/RNTupleWriter), __exit__ method - calls RNTupleReader/RNTupleWriter destructor (if not destructed yet).
tree/ntuple/test/ntuple_basics.py: update tests

This Pull request:

Changes or fixes:

Checklist:

• tested changes locally
• updated the docs (if necessary)

This PR fixes #22431

[jblomer]

@vepadulano @silverweed Your reviews would be useful

[rybkine]

Perhaps, to say the obvious - the proposed implementation is virtually the same as that of the Python file object. And this is exactly what is needed here.

[vepadulano]

I understand the feature request, but I'm not sure deleting the current implementation is the right approach. This PR is modifying quite a few tests which were present before, which is a sign of major changes and thus need to be carefully evaluated. I believe @jblomer and ultimately @silverweed should say whether/how the feature request should be addressed.

[rybkine]

It is not a feature request - it is rather an alternative implementation proposed, which closely follows the implementation in the Python file object. Hence, the changes made.