fix: improve element and node selection handling in post-processing

[germa89]

Description

Fix crashes when having uncomplete selections.

Now, under the hood, for plotting nodes PyMAPDL will select the elements those nodes belong to so we can plot them and avoid crashes.

Issue linked

Close #3782

Checklist

• I have visited and read Develop PyMAPDL.
• I have tested my changes locally
• I have added necessary documentation or updated existing documentation.
• I have followed the PyMAPDL coding style guidelines.
• I have added appropriate unit tests that also ensure the minimal coverage criteria.
• I have reviewed my changes before submitting this pull request.
• I have linked the issue or issues that are solved to the PR if any.
• I have assigned this PR to myself.
• I have marked this PR as draft if it is not ready to be reviewed yet.
• I have made sure that the title of my PR follows Commit naming conventions (e.g. feat: adding new MAPDL command)

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[codecov]

Codecov Report

Attention: Patch coverage is 92.10526% with 3 lines in your changes missing coverage. Please review.

Project coverage is 88.36%. Comparing base (500043e) to head (bb9cb6c).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3784      +/-   ##
==========================================
+ Coverage   88.35%   88.36%   +0.01%     
==========================================
  Files         187      187              
  Lines       14733    14738       +5     
==========================================
+ Hits        13017    13023       +6     
+ Misses       1716     1715       -1     

[germa89]

@pyansys-ci-bot LGTM.

[pyansys-ci-bot]

✅ Approving this PR because germa89 said so in here 😬