Ensure Big Tent uses Goat Rodeo data in tests; solve ground truth data distribution

[dpp]

Two related problems:

1. Ensure Big Tent's tests use data from Goat Rodeo rather than stubs or approximations
2. Solve the ground truth data distribution problem: the dataset is too large for a git repo without LFS, LFS is expensive, and downloading gigabytes from S3 slows CI. Evaluate options (e.g., lazy download, content-addressed caching, split data sets).