fix: send SEP-2243 streamable HTTP headers #2360

Job	Run time
checks / readme-snippets	13s
checks / pre-commit	31s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 4s
checks / test (3.11, lowest-direct, windows-latest)	3m 0s
checks / test (3.10, lowest-direct, windows-latest)	2m 37s
checks / test (3.10, locked, ubuntu-latest)	1m 3s
checks / test (3.10, locked, windows-latest)	2m 33s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 0s
checks / test (3.13, lowest-direct, ubuntu-latest)	59s
checks / test (3.11, locked, ubuntu-latest)	1m 1s
checks / test (3.14, lowest-direct, windows-latest)	2m 34s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 30s
checks / test (3.13, locked, windows-latest)	2m 58s
checks / test (3.12, lowest-direct, windows-latest)	3m 51s
checks / test (3.13, locked, ubuntu-latest)	1m 0s
checks / test (3.12, locked, windows-latest)	3m 19s
checks / test (3.14, locked, windows-latest)	3m 27s
checks / test (3.13, lowest-direct, windows-latest)	3m 35s
checks / test (3.11, locked, windows-latest)	2m 35s
checks / test (3.12, locked, ubuntu-latest)	1m 7s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 13s
checks / test (3.14, locked, ubuntu-latest)	2m 29s
all-green	2s
	43m 41s

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