fix: send SEP-2243 streamable HTTP headers #2547

Job	Run time
checks / readme-snippets	15s
checks / pre-commit	34s
checks / test (3.10, lowest-direct, ubuntu-latest)	56s
checks / test (3.11, lowest-direct, windows-latest)	1m 44s
checks / test (3.11, locked, windows-latest)	1m 18s
checks / test (3.10, locked, windows-latest)	1m 25s
checks / test (3.11, lowest-direct, ubuntu-latest)	49s
checks / test (3.12, lowest-direct, ubuntu-latest)	49s
checks / test (3.12, locked, windows-latest)	1m 25s
checks / test (3.10, locked, ubuntu-latest)	48s
checks / test (3.10, lowest-direct, windows-latest)	1m 29s
checks / test (3.13, lowest-direct, ubuntu-latest)	49s
checks / test (3.11, locked, ubuntu-latest)	49s
checks / test (3.12, locked, ubuntu-latest)	50s
checks / test (3.13, lowest-direct, windows-latest)	1m 41s
checks / test (3.12, lowest-direct, windows-latest)	1m 19s
checks / test (3.14, lowest-direct, ubuntu-latest)	53s
checks / test (3.13, locked, ubuntu-latest)	46s
checks / test (3.13, locked, windows-latest)	1m 15s
checks / test (3.14, locked, ubuntu-latest)	1m 35s
checks / test (3.14, locked, windows-latest)	2m 22s
checks / test (3.14, lowest-direct, windows-latest)	1m 18s
all-green	3s
	25m 12s

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