allow `datetime` after `__init__`

[aaronspring]

Description

• resolves logging error when working with datetime internally after:

# convert to datetime
hindcast._datasets['initialized'] = hindcast._datasets['initialized'].convert_calendar('standard',dim='init')
hindcast._datasets['initialized']['valid_time'] = xr.concat([hindcast._datasets['initialized'].sel(lead=l).swap_dims({'init':'valid_time'}).convert_calendar('standard',dim='valid_time').swap_dims({'valid_time':'init'}).valid_time for l in hindcast._datasets['initialized'].lead],'lead')
hindcast._datasets['observations'] = hindcast._datasets['observations'].convert_calendar('standard',dim='time’)
# now as hindcast._convert_calendar("standard")

• add hindcast._convert_calendar("standard") not a very clean solution - but works for now: a more clean solution would be to allow DatetimeIndex for shift and not converting to CFTimeIndex at __init__

Closes #(issue) @josephhardinee

To-Do List

Type of change

• [x] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• [x] Tests added for pytest, if necessary.

Checklist (while developing)

• [ ] I have added docstrings to all new functions.
• [ ] I have commented my code, particularly in hard-to-understand areas.
• [ ] I have updated the sphinx documentation, if necessary.
• [ ] Any new functions are added to the API. (See contribution guide)
• [ ] CHANGELOG is updated with reference to this PR.

References

[codecov[bot]]

Codecov Report

Merging #742 (bafbe09) into try_logging_only (b2eb8a4) will increase coverage by 0.04%. The diff coverage is 100.00%.

@@                 Coverage Diff                  @@
##           try_logging_only     #742      +/-   ##
====================================================
+ Coverage             92.74%   92.79%   +0.04%     
====================================================
  Files                    59       59              
  Lines                  6186     6201      +15     
====================================================
+ Hits                   5737     5754      +17     
+ Misses                  449      447       -2     

Impacted Files	Coverage Δ
climpred/classes.py	93.47% <100.00%> (+0.07%)	:arrow_up:
climpred/logging.py	93.75% <100.00%> (+15.17%)	:arrow_up:
climpred/tests/test_logging.py	100.00% <100.00%> (ø)

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[aaronspring]

~~checkout on and pip install -e .~~ somehow this is broken