Update conda env yml files and add missing dependencies

[tomvothecoder]

Description

• Closes [Bug]: ModuleNotFoundError: No module named 'xesmf' - using latest main 050d57e #306
• Add xesmf back to the dev.yml
• Add python-dateutil, types-python-dateutil to ci.yml and readthedocs.yml

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

If applicable:

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass with my changes (locally and CI/CD build)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have noted that this is a breaking change for a major release (fix or feature that would cause existing functionality to not work as expected)

[codecov-commenter]

Codecov Report

Merging #307 (3518c21) into main (050d57e) will not change coverage.
The diff coverage is n/a.

❗ Current head 3518c21 differs from pull request most recent head 1dc4511. Consider uploading reports for the commit 1dc4511 to get more accurate results

@@            Coverage Diff            @@
##              main      #307   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
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  Files           14        14           
  Lines         1169      1169           
=========================================
  Hits          1169      1169           

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[tomvothecoder]

@durack1 and @pochedls, this should address the missing xesmf in your dev env now.

I tested it locally and import xcdat, no more missing module.