Use datetime64 natively for particle time throughout codebase (and drop TimeConverter and time_origin) #587

Job	Run time
mypy	3m 33s
py3.13 \| macos \| integration tests	5m 29s
py3.13 \| macos \| unit tests	6h 0m 17s
py3.13 \| ubuntu \| integration tests	5m 8s
py3.13 \| ubuntu \| unit tests	6h 0m 13s
py3.13 \| windows \| integration tests	11m 22s
py3.13 \| windows \| unit tests	8m 2s
py3.10 \| ubuntu \| integration tests	5m 18s
py3.10 \| ubuntu \| unit tests	6h 0m 14s
py3.11 \| ubuntu \| unit tests	6h 0m 14s
py3.12 \| ubuntu \| unit tests	6h 0m 14s
merge-test-artifacts	0s
	1d 6h 40m 4s

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