Refactor `filenames` handling in `Field.from_netcdf` #370

Job	Run time
mypy	3m 53s
py3.13 \| macos \| unit tests	7m 51s
py3.13 \| macos \| integration tests	16m 55s
py3.13 \| ubuntu \| unit tests	13m 3s
py3.13 \| ubuntu \| integration tests	18m 26s
py3.13 \| windows \| unit tests	20m 6s
py3.13 \| windows \| integration tests	31m 32s
py3.10 \| ubuntu \| unit tests	12m 43s
py3.10 \| ubuntu \| integration tests	20m 57s
py3.11 \| ubuntu \| unit tests	12m 46s
py3.12 \| ubuntu \| unit tests	13m 25s
merge-test-artifacts	9s
	2h 51m 46s

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