Make client.py typecheck under pyright #1201

Job	Run time
build-lint-test (3.8, ubuntu-latest)	6m 23s
build-lint-test (3.8, ubuntu-arm)	9m 25s
build-lint-test (3.8, macos-intel)	10m 53s
build-lint-test (3.8, windows-latest)	14m 45s
build-lint-test (3.12, ubuntu-latest)	12m 39s
build-lint-test (3.12, ubuntu-arm)	8m 36s
build-lint-test (3.12, macos-intel)	13m 25s
build-lint-test (3.12, macos-arm)	5m 34s
build-lint-test (3.12, windows-latest)	14m 1s
features-tests / test	6m 23s
	1h 42m 4s

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