Fix various warnings revealed by pytest

[douglatornell]

Most are FutureWarning messages from pandas and xarray. One is an expected PArserWarning from pandas that we now capture and inspect.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 77.64%. Comparing base (650e511) to head (b6aaf10). Report is 24 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #273 +/- ## ======================================= Coverage 77.64% 77.64% ======================================= Files 133 133 Lines 18695 18698 +3 Branches 1910 1911 +1 ======================================= + Hits 14515 14518 +3 Misses 4113 4113 Partials 67 67 ``` | [Flag](https://app.codecov.io/gh/SalishSeaCast/SalishSeaNowcast/pull/273/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=SalishSeaCast) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/SalishSeaCast/SalishSeaNowcast/pull/273/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=SalishSeaCast) | `77.64% <100.00%> (+<0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=SalishSeaCast#carryforward-flags-in-the-pull-request-comment) to find out more.

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