Removing Field.to_write and FieldSet.to_write methods #758

Job	Run time
mypy	3m 35s
py3.13 \| macos \| unit tests	9m 45s
py3.13 \| macos \| integration tests	14m 2s
py3.13 \| ubuntu \| unit tests	9m 46s
py3.13 \| ubuntu \| integration tests	13m 26s
py3.13 \| windows \| unit tests	12m 5s
py3.13 \| windows \| integration tests	24m 7s
py3.10 \| ubuntu \| unit tests	10m 44s
py3.10 \| ubuntu \| integration tests	20m 54s
py3.11 \| ubuntu \| unit tests	10m 13s
py3.12 \| ubuntu \| unit tests	10m 11s
merge-test-artifacts	5s
	2h 18m 53s

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