Small refactors in `particlefile.py` #518

Job	Run time
mypy	3m 58s
py3.13 \| macos \| integration tests	12m 33s
py3.13 \| macos \| unit tests	7m 55s
py3.13 \| ubuntu \| integration tests	25m 39s
py3.13 \| ubuntu \| unit tests	14m 23s
py3.13 \| windows \| integration tests	30m 49s
py3.13 \| windows \| unit tests	19m 44s
py3.10 \| ubuntu \| integration tests	18m 43s
py3.10 \| ubuntu \| unit tests	14m 4s
py3.11 \| ubuntu \| unit tests	13m 41s
py3.12 \| ubuntu \| unit tests	14m 28s
merge-test-artifacts	4s
	2h 56m 1s

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