[tmva] Implementation of a new shuffling strategy in RBatchGenerator

[martinfoell]

This Pull request:

Introduces a new shuffling strategy for creating training batches, ensuring that each batch consists of data from different parts of the RDataFrame. Each chunk loaded into memory, which is used to create batches, now contains blocks of data drawn from different parts of the dataframe.

[github-actions[bot]]

Test Results

    21 files      21 suites   3d 6h 23m 27s ⏱️  3 217 tests  3 217 ✅ 0 💤 0 ❌ 65 834 runs  65 834 ✅ 0 💤 0 ❌

Results for commit 8d8ecf2b.

:recycle: This comment has been updated with latest results.

[martinfoell]

Thank you for your comments @martamaja10 ! I have addressed the comments you gave and added more doxygen comments for the documentation of the functions. I also added more general comments at the beginning of each class to describe what they are used for.