Client notification support #3561

Job	Run time
checks / pre-commit	33s
checks / readme-snippets	14s
checks / test (3.10, highest, windows-latest)	1m 50s
checks / test (3.10, lowest-direct, windows-latest)	1m 57s
checks / test (3.11, lowest-direct, windows-latest)	2m 22s
checks / test (3.11, highest, ubuntu-latest)	40s
checks / test (3.11, highest, windows-latest)	2m 3s
checks / test (3.11, lowest-direct, ubuntu-latest)	40s
checks / test (3.10, lowest-direct, ubuntu-latest)	44s
checks / test (3.12, highest, ubuntu-latest)	45s
checks / test (3.12, lowest-direct, windows-latest)	2m 59s
checks / test (3.13, highest, windows-latest)	2m 0s
checks / test (3.12, lowest-direct, ubuntu-latest)	46s
checks / test (3.13, lowest-direct, ubuntu-latest)	46s
checks / test (3.10, highest, ubuntu-latest)	44s
checks / test (3.13, lowest-direct, windows-latest)	2m 9s
checks / test (3.13, highest, ubuntu-latest)	42s
checks / test (3.12, highest, windows-latest)	2m 59s
	24m 53s

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