Refactor `filenames` handling in `Field.from_netcdf` #359

Job	Run time
mypy	3m 41s
py3.13 \| macos \| integration tests	14m 14s
py3.13 \| ubuntu \| integration tests	19m 37s
py3.13 \| windows \| integration tests	33m 53s
py3.13 \| macos \| unit tests	10m 48s
py3.10 \| ubuntu \| integration tests	18m 19s
py3.13 \| ubuntu \| unit tests	13m 1s
py3.13 \| windows \| unit tests	20m 43s
py3.10 \| ubuntu \| unit tests	12m 41s
py3.11 \| ubuntu \| unit tests	12m 40s
py3.12 \| ubuntu \| unit tests	13m 47s
merge-test-artifacts	2s
	2h 53m 26s

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