Miles30/fix datagen hang

[PatrickRMiles]

Fixes a dataset generation hang in scaffold generate_fractals.

• Corrects the fractal category acceptance check to measure variance across the point cloud's x/y/z dimensions instead of across coordinates within each point.
• Rejects non-finite point clouds before normalization and improves category-search progress/accounting output.
• Updates job scripts to pass an absolute --fract-base-dir, so torchrun-hpc launch directories do not hide the existing fractal category files.