docs: add missing docstrings to core client/server session API methods #2381

Job	Run time
checks / readme-snippets	10s
checks / pre-commit	39s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 7s
checks / test (3.10, lowest-direct, windows-latest)	3m 7s
checks / test (3.10, locked, windows-latest)	2m 32s
checks / test (3.10, locked, ubuntu-latest)	1m 0s
checks / test (3.11, locked, windows-latest)	2m 47s
checks / test (3.11, locked, ubuntu-latest)	1m 4s
checks / test (3.12, lowest-direct, windows-latest)	4m 4s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 5s
checks / test (3.11, lowest-direct, windows-latest)	3m 19s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 13s
checks / test (3.12, locked, ubuntu-latest)	1m 8s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 4s
checks / test (3.13, lowest-direct, windows-latest)	2m 39s
checks / test (3.12, locked, windows-latest)	4m 12s
checks / test (3.13, locked, ubuntu-latest)	1m 0s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 31s
checks / test (3.14, locked, windows-latest)	3m 18s
checks / test (3.13, locked, windows-latest)	2m 23s
checks / test (3.14, lowest-direct, windows-latest)	3m 9s
checks / test (3.14, locked, ubuntu-latest)	2m 37s
all-green	4s
	45m 12s

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