Release 3.1.0

[jpata]

• run a checkpoint training for CLIC and CLD with 500k events per dataset (ongoing)

$ ls -lrt experiments
pyg-cld-v1_cld_20260328_101206_533260
pyg-cld-hits-v1_cld_20260328_101205_900871
pyg-clic-v1_clic_20260328_101206_529710
pyg-clic-hits-v1_clic_20260328_101207_247756

• run a high-stats validation for both CLIC and CLD
• upload models to huggingface as 3.1.0
• ensure PyPI is configured to accept the tag (so far, TestPyPI worked OK)
• tag release 3.1.0 and ensure it gets uploaded to PyPI