fieldfilebuffer.py cleanup #638

Job	Run time
mypy	3m 27s
py3.13 \| macos \| integration tests	11m 53s
py3.13 \| macos \| unit tests	8m 18s
py3.13 \| ubuntu \| integration tests	20m 42s
py3.13 \| ubuntu \| unit tests	9m 31s
py3.13 \| windows \| integration tests	21m 50s
py3.13 \| windows \| unit tests	10m 51s
py3.10 \| ubuntu \| integration tests	14m 15s
py3.10 \| ubuntu \| unit tests	10m 32s
py3.11 \| ubuntu \| unit tests	9m 43s
py3.12 \| ubuntu \| unit tests	9m 44s
merge-test-artifacts	2s
	2h 10m 48s

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