feat: allow overriding SSE messages endpoint #2044

Job	Run time
checks / readme-snippets	10s
checks / pre-commit	37s
checks / test (3.10, lowest-direct, ubuntu-latest)	51s
checks / test (3.11, lowest-direct, windows-latest)	2m 44s
checks / test (3.11, locked, windows-latest)	2m 35s
checks / test (3.11, locked, ubuntu-latest)	50s
checks / test (3.10, locked, windows-latest)	2m 59s
checks / test (3.10, lowest-direct, windows-latest)	2m 27s
checks / test (3.11, lowest-direct, ubuntu-latest)	49s
checks / test (3.10, locked, ubuntu-latest)	46s
checks / test (3.13, lowest-direct, ubuntu-latest)	47s
checks / test (3.12, locked, windows-latest)	3m 25s
checks / test (3.12, locked, ubuntu-latest)	55s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 13s
checks / test (3.12, lowest-direct, windows-latest)	3m 20s
checks / test (3.13, lowest-direct, windows-latest)	2m 40s
checks / test (3.14, lowest-direct, windows-latest)	2m 24s
checks / test (3.13, locked, windows-latest)	2m 37s
checks / test (3.12, lowest-direct, ubuntu-latest)	56s
checks / test (3.13, locked, ubuntu-latest)	47s
checks / test (3.14, locked, ubuntu-latest)	2m 14s
checks / test (3.14, locked, windows-latest)	3m 0s
all-green	3s
	39m 9s

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