Use element indices `particle.ei` in curvilinear search #1435

Job	Run time
py3.12 \| ubuntu \| unit tests	5m 45s
py3.11 \| ubuntu \| unit tests	5m 30s
mypy	0s
py${{ matrix.python-version }} \| ${{ matrix.os }} \| integration tests	0s
merge-test-artifacts	-1s
	11m 14s

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