Make test suite fail on warnings

[enzbus]

Some individual test modules enforce warnings='error' in unittest.main but that is not done in __main__.py. Most warnings have been fixed already, with this we'll get a Github CI failure any time, e.g., a dependency update introduces a deprecation warning.

Pandas 2.2.0 introduces a future warning regarding Pyarrow becoming a dependency. We could add a Parquet loader/storer function to the data module as part of PR #127 .