make meshio an optional dependency

[nschloe]

Fixes #1938.

[github-actions]

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[codecov]

Codecov Report

Merging #1939 (0c4278b) into main (9849318) will decrease coverage by 0.00%.
The diff coverage is 14.28%.

@@            Coverage Diff             @@
##             main    #1939      +/-   ##
==========================================
- Coverage   29.74%   29.73%   -0.01%     
==========================================
  Files          72       72              
  Lines       14111    14112       +1     
==========================================
- Hits         4197     4196       -1     
- Misses       9914     9916       +2     

[banesullivan]

Just an FYI if this merges, we need to update the conda-forge recipe

[akaszynski]

Just an FYI if this merges, we need to update the conda-forge recipe

Will do on the next release. Thanks for the reminder.