`load_samples.py` - Githubissues

Summary Change Description

Added the command line script to load samples from the new samples loader code.

Details:

Added types-python-dateutil to the dev requirements (based on mypy suggestion).
Created fallback methods for parsing dates in string_to_datetime, based on parsing done in the old sample_table_loader.
Added a required values check to the animals loader tests.
Added clarifying messages to the min/max value validators for Sample.time_collected.
Fixed the samples_loader time_collected units from days to minutes.
Made load_table provide keep_default_na as True if dtypes are supplied and contain non-string types.
Made none_vals a class attribute in TableLoader so that check_dataframe_values would not report duplicate values when the value is "nan".
Removed the column type for DATE_KEY in the samples loader, so that pandas would auto-detect dates. (There is likely a better type to assign, but I just haven't looked into it yet, as it's not a priority.)
Pinned numpy at 1.26.4 to address an import error via chempy that is related to the nupy release yesterday of 2.0.0. I reported the issue to the chempy repo and they're on it.

See comments in-line.

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