Make client.py typecheck under pyright #1200

Job	Run time
build-lint-test (3.8, ubuntu-latest)	1m 15s
build-lint-test (3.8, ubuntu-arm)	2m 37s
build-lint-test (3.8, macos-intel)	2m 17s
build-lint-test (3.8, windows-latest)	1m 28s
build-lint-test (3.12, ubuntu-latest)	1m 48s
build-lint-test (3.12, ubuntu-arm)	2m 37s
build-lint-test (3.12, macos-intel)	2m 54s
build-lint-test (3.12, macos-arm)	1m 24s
build-lint-test (3.12, windows-latest)	4m 23s
features-tests / test	5m 45s
	26m 28s

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