refactor: connect-first stream lifecycle for sse and streamable_http #1474

Job	Run time
checks / readme-snippets	14s
checks / pre-commit	38s
checks / test (3.10, locked, windows-latest)	2m 14s
checks / test (3.10, locked, ubuntu-latest)	51s
checks / test (3.11, locked, ubuntu-latest)	49s
checks / test (3.10, lowest-direct, windows-latest)	2m 40s
checks / test (3.11, lowest-direct, windows-latest)	2m 52s
checks / test (3.10, lowest-direct, ubuntu-latest)	55s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 0s
checks / test (3.11, locked, windows-latest)	3m 24s
checks / test (3.14, locked, ubuntu-latest)	2m 19s
checks / test (3.13, lowest-direct, ubuntu-latest)	54s
checks / test (3.13, lowest-direct, windows-latest)	2m 43s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 4s
checks / test (3.14, locked, windows-latest)	3m 4s
checks / test (3.14, lowest-direct, windows-latest)	2m 26s
checks / test (3.12, lowest-direct, windows-latest)	3m 37s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 21s
checks / test (3.12, locked, windows-latest)	3m 23s
checks / test (3.13, locked, windows-latest)	2m 26s
checks / test (3.12, locked, ubuntu-latest)	54s
checks / test (3.13, locked, ubuntu-latest)	47s
all-green	4s
	40m 39s

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