Add MineRL/BASALT trajectory converter

[mkdsrt10]

Summary

Adds opt-in MineRL/BASALT support that streams demonstration trajectories directly into Stable World Model’s Lance layout.

• adds swm convert-minerl for MineRL/BASALT demonstrations
• stores RGB POV observations, deterministic flattened numeric actions, rewards, done flags, episode IDs, and timesteps
• adds a lazy MineRL environment factory
• keeps MineRL optional through a dedicated minerl extra
• documents the conversion workflow and adds unit tests using a mock pipeline (no Minecraft runtime required)

Validation

• PYTHONPATH=. pytest -q tests/data/test_minerl_converter.py (3 passed)
• PYTHONPATH=. python -m stable_worldmodel.cli --help (verifies convert-minerl registration)

This deliberately excludes MineJEPA training, checkpoints, experiments, and model-specific tooling so the contribution remains a reusable data/framework extension.

[lucas-maes]

Hi ty very much for you PR! However I think it would be more relevant to add it to stable-dataset another effort made by this research group!

I'll close this PR, feel free to open a new one on stable-datasets directly!

[mkdsrt10]

Thank you for the guidance, Lucas. That makes sense—I will adapt this into a focused MineRL integration for stable-datasets and open a new PR there. I appreciate the direction.

[mkdsrt10]

Follow-up: I moved the integration to stable-datasets as suggested: galilai-group/stable-datasets#67

It adds a focused MineRLTreechop transition dataset builder. I also validated it against locally acquired MineRLTreechop-v0 data: 209 trajectories discovered, and one real trajectory cached end-to-end as 2,122 rows with 64x64 RGB observations and 10-D flattened actions. Thank you again for pointing me to the right home for this contribution.