Absolute import instead of relative

[ahijevyc]

For 3 scripts in metplotpy/contributed/fv3_physics_tend...

Follow the style of metplotpy module importing that is used in metplotpy/contributed/stratosphere_diagnostics/stratosphere_diagnostics.py to avoid error about relative import.

In other words, replace from . import physics_tend
with import metplotpy.contributed.fv3_physics_tend.physics_tend

That should avoid the
ImportError: attempted relative import with no known parent package.

Pull Request Testing

• Describe testing already performed for these changes:
  

It works in a conda environment with metplotpy 2.1.0

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  

setenv METPLOTPY_BASE <path>
setenv CONFIG $METPLOTPY_BASE/test/fv3_physics_tend/fv3_physics_tend_defaults.yaml
setenv WORKING_DIR $METPLOTPY_BASE/metplotpy/contributed/fv3_physics_tend
cd $WORKING_DIR
python planview_fv3.py -h

• Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [Yes]

• Do these changes include sufficient testing updates? [Yes]

• Will this PR result in changes to the test suite? [No]
  
  If yes, describe the new output and/or changes to the existing output:
  

• Do these changes introduce new SonarQube findings? [No]
  
  If yes, please describe:

• Please complete this pull request review by [February 2025].
  

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