fix time_bnds issue

[rhaegar325]

This pull request addresses and resolves issue #141 .

It updates the coordinate-handling step to ensure that time_bnds is preserved in the ocean variable cmorisation output.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.92%. Comparing base (77d2538) to head (feb1268).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/access_moppy/ocean.py	0.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #142      +/-   ##
==========================================
+ Coverage   57.64%   57.92%   +0.27%     
==========================================
  Files          18       18              
  Lines        2399     2403       +4     
==========================================
+ Hits         1383     1392       +9     
+ Misses       1016     1011       -5     

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