[ntuple] Fields tree as dot

[magnustymoteus]

This Pull request:

Changes or fixes:

This PR introduces the method RNTupleInspector::GetFieldsTreeAsDot which gives a string that represents the tree structure of RNTuple fields in .dot language (that can then be displayed in graphviz for example)

Checklist:

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

[silverweed]

Very nice, thanks! I left a couple of comments.
Also, do you have maybe a screenshot of an example rendered output?

[magnustymoteus]

This is an example of graphviz's rendered output (where Placeholder is a user-defined class containing an integer and a float)

This is obviously very rudimentary right now, but I can work on expanding this today.

[github-actions]

Test Results

    21 files      21 suites   3d 16h 36m 52s ⏱️
 3 203 tests  3 198 ✅ 0 💤  5 ❌
65 594 runs  65 584 ✅ 0 💤 10 ❌

For more details on these failures, see this check.

Results for commit 5294d78.

♻️ This comment has been updated with latest results.

[magnustymoteus]

This is the new rendered output with the same example:

Additionally, I removed the (tabular) styling to keep it simple.

[silverweed]

Looks good! Just a couple more things before we merge

[silverweed]

LGTM, thanks!

[vepadulano]

Very nice work! Can I suggest to clean the commit history before merging? That would include squashing formatting/small fixes commits together in one (or a few) main commits and using our convention for the commit message e.g.

[ntuple] VERB_IMPERATIVE_FORM description_of_commit_objective

[enirolf]

Very nice work! I have some small nitpicks to address before merging, but after that it's good to go from my side :).

[magnustymoteus]

The requested changes should be implemented, I'll squash the commits now.

[enirolf]

Thank you for the changes, LGTM!