add: regen.py (main hyperparameter training file)

feat: add utility functions for fiber dataset visualization and hyperparameter training;
housekeeping: rename dataset.py -> datasets.py

src/single-core-regen/util/__init__.py

@@ -0,0 +1,3 @@
+from .datasets import FiberRegenerationDataset  # noqa: F401
+from .optuna_vis import show_figures # noqa: F401
+from .plot import eye # noqa: F401