[RF] ToyMCSampler improvements for binned toys

[cburgard]

This Pull request:

Adds the ability to control the ToyMCSampler to emit binned toys.
Makes use of this new capability in the HypoTestCalculator in cases where the observed data is binned.

Checklist:

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

This PR fixes #

[cburgard]

This PR is still WIP. This is because the use case relies on #20097 being merged first (even though the functionalities are not closely related).

[guitargeek]

I have merged #20097. Could you please rebase this PR?

Also, could you please add a commit where you add both of you to the list of contributors for ROOT 6.38 (insert in alphabetical order)?
https://github.com/root-project/root/blob/master/README/ReleaseNotes/v638/index.md

Thanks a lot!

[github-actions]

Test Results

    22 files      22 suites   3d 19h 35m 46s ⏱️
 3 692 tests  3 684 ✅ 0 💤   8 ❌
79 273 runs  79 097 ✅ 0 💤 176 ❌

For more details on these failures, see this check.

Results for commit fbb3468.

[cburgard]

I have merged #20097. Could you please rebase this PR?

Also, could you please add a commit where you add both of you to the list of contributors for ROOT 6.38 (insert in alphabetical order)? https://github.com/root-project/root/blob/master/README/ReleaseNotes/v638/index.md

Thanks a lot!

Thanks a lot!

Done and done. I've removed the WIP marker now.