fix: send SEP-2243 streamable HTTP headers #2359

Job	Run time
checks / readme-snippets	13s
checks / pre-commit	33s
checks / test (3.11, lowest-direct, windows-latest)	3m 23s
checks / test (3.10, locked, windows-latest)	2m 49s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 4s
checks / test (3.12, lowest-direct, windows-latest)	4m 15s
checks / test (3.11, lowest-direct, ubuntu-latest)	52s
checks / test (3.12, locked, windows-latest)	3m 55s
checks / test (3.10, lowest-direct, windows-latest)	3m 6s
checks / test (3.10, locked, ubuntu-latest)	1m 0s
checks / test (3.14, lowest-direct, windows-latest)	2m 43s
checks / test (3.12, locked, ubuntu-latest)	56s
checks / test (3.11, locked, windows-latest)	2m 44s
checks / test (3.13, lowest-direct, windows-latest)	3m 7s
checks / test (3.13, locked, windows-latest)	3m 19s
checks / test (3.10, lowest-direct, ubuntu-latest)	53s
checks / test (3.11, locked, ubuntu-latest)	52s
checks / test (3.13, lowest-direct, ubuntu-latest)	51s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 25s
checks / test (3.13, locked, ubuntu-latest)	53s
checks / test (3.14, locked, ubuntu-latest)	2m 7s
checks / test (3.14, locked, windows-latest)	3m 59s
all-green	3s
	45m 2s

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