* [Fix] Pandas 3 string type handling
* [ci] Temporarily remove WError because of scipy deprecation
* [Fix] Address edge cases in _deserialize_df
- Use pd.isna() instead of truthiness check for gzip null guard, fixing
incorrect behavior when null is np.nan (which is truthy in Python)
- Add bounds check to while loop to prevent IndexError when all non-null
values are empty strings converted to None by regex replace
* [Fix] Address edge cases in _deserialize_df and add string dtype tests
- Guard against IndexError on empty DataFrames and all-null columns
- Use is not None instead of pd.isna() for Obs objects in auto_gamma
- Add tests for string dtype columns (with/without None, CSV and SQL)
- Add test for empty DataFrame deserialization
* [Fix] Avoid skipping NA-to-None conversion and guard auto_gamma against None lists
- Replace continue with conditional to preserve NA-to-None conversion for all-null columns
- Guard auto_gamma list lambda against None values to prevent TypeError
- Add tests for all-empty-string columns and Obs lists with None + auto_gamma
* corret type clause
* add tests, changes in create_json_string
* create json-string now gives back None
* revert changes
* fix panda sql export
* add SQL test
* fixed None type export for csv and sql.gz
* move None parsing to json io
* alter regex
* revert changes
* only replace None with empty str when necessary
* fixed deserialze_df for python 3.7
* add more tesets
* fix case where gz was ignored
* hand voer gz explicitly
* replace nan by None in non-Obs columns
* moved warning to csv export, mroe tests
* only values able to be nan are put in np.isnan()
* added python float for warning
* feat: Added serialization of list of Obs in pandas.to_sql.
* tests: test for list of Obs to sql added.
* feat: auto_gamma functionality added for deserialization of lists of
Obs.
