Client notification support #4022

Job	Run time
checks / pre-commit	31s
checks / readme-snippets	14s
checks / test (3.10, lowest-direct, windows-latest)	2m 29s
checks / test (3.10, lowest-direct, ubuntu-latest)	48s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 9s
checks / test (3.11, lowest-direct, windows-latest)	2m 30s
checks / test (3.12, lowest-direct, ubuntu-latest)	50s
checks / test (3.10, highest, windows-latest)	2m 40s
checks / test (3.11, highest, windows-latest)	2m 55s
checks / test (3.12, highest, ubuntu-latest)	53s
checks / test (3.12, highest, windows-latest)	4m 2s
checks / test (3.12, lowest-direct, windows-latest)	4m 23s
checks / test (3.11, highest, ubuntu-latest)	49s
checks / test (3.14, lowest-direct, windows-latest)	2m 4s
checks / test (3.13, lowest-direct, windows-latest)	2m 41s
checks / test (3.11, lowest-direct, ubuntu-latest)	47s
checks / test (3.13, highest, windows-latest)	2m 59s
checks / test (3.10, highest, ubuntu-latest)	48s
checks / test (3.13, lowest-direct, ubuntu-latest)	46s
checks / test (3.14, highest, ubuntu-latest)	1m 11s
checks / test (3.14, highest, windows-latest)	2m 21s
checks / test (3.13, highest, ubuntu-latest)	45s
	38m 35s

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