Saved models overwrite each other across paradigms and suffixes

[kalomak]

Problem

With save_model=True in evaluations, models go to <hdf5_path>/<GridSearch|Models>_<eval>/<dataset>/<subject>/<session>/<pipeline>/. The path doesn't include the paradigm or suffix, so two runs that differ only in those overwrite each other's models.

Possible fixes

1. Minimal: add <Paradigm>/<suffix> after <GridSearch|Models>_<eval>/.
2. Unified: Mirror the results layout more closely, something like:<hdf5_path>/models/<Paradigm>/<Evaluation>/models_<suffix>/<dataset>/<subject>/<session>/<pipeline>/ .

Both change existing model paths so breaking change.

[lindicaphxag-tech]

I implemented the minimal layout proposed here in PR #1206: Models_<evaluation>/<Paradigm>/<suffix-if-set>/<dataset>/<subject>/<session>/<pipeline>/. Evaluation saves now pass paradigm and suffix through both the parallel and legacy paths; direct calls to the private helper without a paradigm keep the previous layout. The focused path/integration tests pass (11 passed), and the changelog calls out the path compatibility change. If you had a different path migration preference, I can adjust the PR.