Fill `containers.SimulatedCameraContainer.true_image_sum` in HDF5eventsource #5095

Job	Run time
docs	9m 27s
lint	20s
tests (Linux (3.10, mamba), ubuntu-latest, 3.10, mamba, tests,all)	12m 8s
tests (Linux (3.10, pip), ubuntu-latest, 3.10, pip, tests,all)	13m 14s
tests (Linux (3.11, pip, minimal-dependencies), ubuntu-latest, 3.11, pip, tests)	11m 34s
tests (Linux (3.12, mamba, coverage), ubuntu-latest, 3.12, mamba, codecov, tests,all)	12m 57s
tests (Linux (3.12, pip), ubuntu-latest, 3.12, pip, tests,all)	14m 11s
tests (macos (3.10, x86_64, pip), macos-13, 3.10, pip, tests,all)	14m 30s
tests (macos (3.12, arm64, mamba), macos-14, 3.12, mamba, tests,all)	11m 27s
	1h 39m 48s

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