ENH: Improve vline #1070

Job	Run time
PyQt5 / ubuntu	2m 34s
PyQt6 / ubuntu	6m 59s
PySide2 / ubuntu	3m 22s
PySide6 / ubuntu	9m 37s
PySide6 / macos	12m 46s
PySide6 / windows	11m 28s
pytest matrix / ubuntu / MNE main	3m 3s
pytest matrix / ubuntu / MNE maint/1.4	2m 47s
pytest matrix / windows / MNE main	3m 49s
pytest matrix / windows / MNE maint/1.4	8m 47s
pytest matrix / macos / MNE main	4m 20s
pytest matrix / macos / MNE maint/1.4	6m 57s
pytest old 3.8 / ubuntu / MNE main	4m 4s
pytest no opengl / ubuntu / MNE main	3m 7s
pytest no opengl / ubuntu / MNE maint/1.4	2m 54s
pytest old / ubuntu / MNE maint/1.3	2m 48s
pytest pip-pre / ubuntu / MNE main	3m 25s
	1h 32m 47s

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