Add `dt` to TSM

[sjordan29]

Addressing #79 with a quick fix. This adds a dt variable to TSM, with a default at 1 day to be consistent with NSM. When we merge this PR, we should open an issue to formalize time handling (potentially using xarray simlab).

• The test comparing the calculations sets this dt parameter at 1/86400 days (1 second) and we get the correct output
• I updated the notebooks to demonstrate how to use dt.

[sjordan29]

Looks like the tests that were failing were remnants of #87, which we discussed and were OK with failing.

I added the @pytest.mark.xfail(reason="Known issue with kbod 20 test TBA.") decorator to these. This should ensure the pipeline passes but still flags the failing tests. Can @imscw95 or @aufdenkampe open an issue detailing the status of the test that's failing?

[codecov[bot]]

Codecov Report

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

Project coverage is 89.13%. Comparing base (ca28ae8) to head (eaf0b58). Report is 37 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #89 +/- ## ========================================== + Coverage 80.62% 89.13% +8.50% ========================================== Files 27 25 -2 Lines 1843 1712 -131 ========================================== + Hits 1486 1526 +40 + Misses 357 186 -171 ```

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[sjordan29]

I'll be out of office until 9/12. @imscw95, if you get a chance to review and all looks OK - feel free to merge to main. Otherwise, we can resolve when I return. Thanks!