feat(client): add validate_structured_output option to ClientSession #2519

Job	Run time
checks / pre-commit	30s
checks / readme-snippets	11s
checks / test (3.10, locked, windows-latest)	1m 14s
checks / test (3.10, lowest-direct, windows-latest)	1m 15s
checks / test (3.11, lowest-direct, windows-latest)	1m 20s
checks / test (3.11, locked, windows-latest)	1m 13s
checks / test (3.10, locked, ubuntu-latest)	49s
checks / test (3.14, lowest-direct, ubuntu-latest)	35s
checks / test (3.14, locked, ubuntu-latest)	1m 52s
checks / test (3.11, locked, ubuntu-latest)	48s
checks / test (3.10, lowest-direct, ubuntu-latest)	52s
checks / test (3.12, lowest-direct, ubuntu-latest)	50s
checks / test (3.12, lowest-direct, windows-latest)	1m 33s
checks / test (3.13, lowest-direct, ubuntu-latest)	55s
checks / test (3.14, lowest-direct, windows-latest)	1m 7s
checks / test (3.11, lowest-direct, ubuntu-latest)	50s
checks / test (3.14, locked, windows-latest)	1m 58s
checks / test (3.13, locked, windows-latest)	1m 17s
checks / test (3.12, locked, windows-latest)	1m 17s
checks / test (3.13, lowest-direct, windows-latest)	1m 46s
checks / test (3.13, locked, ubuntu-latest)	46s
checks / test (3.12, locked, ubuntu-latest)	54s
all-green	4s
	23m 56s

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