Fix plotting interpolation bug with spatial variables

[MarcBerliner]

Description

When the time axis changes scale (e.g., from seconds to hours or days), minor floating-point arithmetic issues at the initial and final times can cause interpolation outside the timespan. As a result, the spatial variables could return NaN at the initial and final time points

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #)

Important checks:

Please confirm the following before marking the PR as ready for review:

• No style issues: nox -s pre-commit
• All tests pass: nox -s tests
• The documentation builds: nox -s doctests
• Code is commented for hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.70%. Comparing base (2803090) to head (5cee466).
Report is 87 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #4841   +/-   ##
========================================
  Coverage    98.70%   98.70%           
========================================
  Files          303      303           
  Lines        23328    23335    +7     
========================================
+ Hits         23025    23032    +7     
  Misses         303      303           

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