S3 support

[crusaderky]

recursive_diff, recursive_eq, and the recursive-diff CLI all already support s3:// URLs to single NetCDF or Zarr files.
Must add:

• support for globbing (recursive_open and recursive-diff -r CLI)
• support for opening JSON, JSONL, MessagePack, and YAML files over s3://
• unit tests (must not require actual s3 access)
• pip optional dependencies