Remove deferred loading of FieldSets #675

Job	Run time
mypy	3m 17s
py3.13 \| macos \| unit tests	8m 2s
py3.13 \| macos \| integration tests	15m 4s
py3.13 \| ubuntu \| unit tests	9m 44s
py3.13 \| ubuntu \| integration tests	17m 25s
py3.13 \| windows \| unit tests	12m 51s
py3.13 \| windows \| integration tests	28m 42s
py3.10 \| ubuntu \| unit tests	10m 26s
py3.10 \| ubuntu \| integration tests	17m 35s
py3.11 \| ubuntu \| unit tests	9m 35s
py3.12 \| ubuntu \| unit tests	9m 49s
merge-test-artifacts	2s
	2h 22m 32s

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