[Geom] Add auxiliary user-data export in TGDMLWrite

[KoljaFrahm]

This Pull request:

Adds the option of exporting auxiliary of TGeoVolumes in TGDMLWrite
Uses same format as in https://github.com/root-project/root/blob/master/geom/gdml/src/TGDMLParse.cxx

Changes or fixes:

Fixes #20356

Checklist:

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

This PR fixes #20356

[KoljaFrahm]

I reformatted my commit (clang), do I still have to do so something to start the tests again?

[dpiparo]

Is there a way in which we could test this fix?

[KoljaFrahm]

I described two ways in the issues (Reproducer).
Is this enough or should I describe something in more detail?

[KoljaFrahm]

I am not sure why the ruff code analysis fails for files I haven't changed

[agheata]

Thanks @KoljaFrahm for this addition - reading the auxiliary data via TGDMLParse was only intended so far to provide user access to these data via the volume user extensions, but it is indeed nice to be able to re-export it. See my comment requesting a small correction - otherwise your patch works nicely!

[agheata]

Is there a way in which we could test this fix?

Actually, this is not a fix but a feature, allowing the re-export of GDML auxiliary volume data imported from a GDML file. It could be tested eventually if we make a more general GDML import/export regression test

[KoljaFrahm]

Adjusted and rebased :)

[KoljaFrahm]

Is still something missing from my side? Would be nice to have this in the next root version :)

[dpiparo]

I propose to have these changes integrated in the main branch as soon as the tests passes.
Then, if @agheata agrees, we could potentially think of having it integrated in the v6-38-00-patches branch to have it available in 6.38.02, likely available in a few weeks from now...

[KoljaFrahm]

That would be great!

[github-actions]

Test Results

    22 files      22 suites   3d 20h 27m 42s ⏱️
 3 777 tests  3 775 ✅ 0 💤 2 ❌
81 184 runs  81 182 ✅ 0 💤 2 ❌

For more details on these failures, see this check.

Results for commit 30ef55c.