Small refactors in `particlefile.py` #516

Job	Run time
mypy	4m 26s
py3.13 \| macos \| integration tests	1m 46s
py3.13 \| macos \| unit tests	2m 5s
py3.13 \| ubuntu \| integration tests	17m 21s
py3.13 \| ubuntu \| unit tests	14m 10s
py3.13 \| windows \| integration tests	29m 17s
py3.13 \| windows \| unit tests	20m 29s
py3.10 \| ubuntu \| integration tests	29m 11s
py3.10 \| ubuntu \| unit tests	13m 55s
py3.11 \| ubuntu \| unit tests	13m 26s
py3.12 \| ubuntu \| unit tests	14m 37s
merge-test-artifacts	0s
	2h 40m 43s

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