Improve file writing

[gerlero]

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 86.69%. Comparing base (83e52a1) to head (784e910).

Files with missing lines	Patch %	Lines
foamlib/_files/_serialization.py	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #258      +/-   ##
==========================================
+ Coverage   86.59%   86.69%   +0.09%     
==========================================
  Files          16       16              
  Lines        1343     1345       +2     
==========================================
+ Hits         1163     1166       +3     
+ Misses        180      179       -1     

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