silx.gui: support imageaggregate in _plot2d #1688

Job	Run time
Python 3.8 on ubuntu-20.04 PyQt5	10m 15s
Python 3.11 on ubuntu-latest PyQt6	9m 26s
Python 3.12 on ubuntu-latest PySide6	6m 55s
Python 3.10 on macos-13 PyQt5	16m 31s
Python 3.12 on macos-13 PyQt6	15m 35s
Python 3.9 on macos-13 PySide6	9m 23s
Python 3.9 on windows-latest PyQt5	9m 25s
Python 3.12 on windows-latest PyQt6	9m 50s
Python 3.10 on windows-latest PySide6	4m 34s
	1h 31m 54s

Provide feedback