Update to newest version of ESS-DIVE Dataset API

[caufieldjh]

This pull request improves the handling of authentication for ESS-DIVE metadata access, making public metadata retrieval possible without a token and clarifying related documentation and error handling. The code now gracefully supports both anonymous and authenticated requests, and the test suite has been expanded to verify these behaviors.

Authentication and API request handling:

• Refactored the ESS-DIVE API wrapper (essdive.py) to allow anonymous public metadata access by omitting the Authorization header when no valid token is provided. Added helper functions normalize_essdive_token and _essdive_headers for robust token normalization and header construction. The API now accepts both DOI and ESS-DIVE package identifiers and correctly encodes them for requests. [1] [2] [3] [4]

CLI and error handling improvements:

• Removed mandatory token checks from the CLI (cli.py), so commands no longer fail if ESSDIVE_TOKEN is unset, enabling public metadata retrieval without authentication. [1] [2]

Documentation updates:

• Updated README.md to clarify that a token is only needed for non-public datasets, revised environment variable instructions, and improved troubleshooting guidance for authenticated access. [1] [2] [3] [4]

Testing enhancements:

• Expanded the test suite (test_essdive_api.py) to cover anonymous access, token normalization, inclusion/omission of the Authorization header, and support for both DOI and ESS-DIVE package identifiers. [1] [2] [3]