Support RNTuple as possible output format

[ponyisi]

• Support RNTuple as output format for the uproot-raw and func_adl_uproot transformers
  • Add necessary enums; update uproot-raw transformer
• uproot 5.6 doesn't yet implement compression when writing RNTuple, so this option is not yet recommended for production.

[ponyisi]

Good to go here I think for RNTuple output (see #999). I do not recommend rntuple yet (uproot does not yet have compression enabled for the output in 5.6.0) but the code paths technically work and produce correct output.

[Copilot]

Copilot reviewed 6 out of 7 changed files in this pull request and generated no comments.

Files not reviewed (1)

• code_generator_raw_uproot/transformer_capabilities.json: Language not supported

Comments suppressed due to low confidence (2)

code_generator_raw_uproot/servicex/templates/transform_single_file.py:29

• In the root-file branch, the previous conditional that checked if v[0].fields existed was removed. Consider reinstating or handling the case where v[0].fields might be empty to avoid potential runtime errors.

if output_format in ('root-file', 'root-rntuple'):

code_generator_raw_uproot/servicex/raw_uproot_code_generator/request_translator.py:150

• The change from constructing a dict of field types to directly returning arr.layout may affect consumers expecting a specific structure. Ensure that downstream code is compatible with this new format.

rv_arrays_trees[outtreename] = (None, arr.layout)

[gordonwatts]

Huh - copilot is now reviewing our PRs!

Ok - this looks fine - My only comments are style comments (nested if statements, etc.). I also cleaned up the PR text because it is often used to generate change logs. I'll mark approve, but you might made modifications regardless.

[ponyisi]

I should note that the next uproot release will remove the need for funny ListArray manipulation and will compress the RNTuples, so it makes sense to hold off on this PR until we get the new version. (The code here should still work with the new release but will have code branches that are no longer relevant.)

[BenGalewsky]

Excellent