Support writing binary fields

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 60.00000% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 88.79%. Comparing base (60d3155) to head (29bc6bf).

Files	Patch %	Lines
foamlib/_files/_serialization.py	52.94%	8 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #95 +/- ## ========================================== - Coverage 89.01% 88.79% -0.23% ========================================== Files 10 10 Lines 792 803 +11 ========================================== + Hits 705 713 +8 - Misses 87 90 +3 ```

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