Refactor serialization

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 85.00000% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 89.76%. Comparing base (07d6a50) to head (9f92447).

Files	Patch %	Lines
foamlib/_files/_serialization.py	84.21%	6 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #88 +/- ## ========================================== + Coverage 89.36% 89.76% +0.40% ========================================== Files 10 10 Lines 799 762 -37 ========================================== - Hits 714 684 -30 + Misses 85 78 -7 ```

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