refactor(streamable_http): remove writer notification on ClientDisconnect#6

wiggzz wants to merge 2 commits intodbt-labs/patched-1.27.0dbt-labs/mcp-python-sdk:dbt-labs/patched-1.27.0from

wj/DI-3218-lowlevel-disconnect-debugdbt-labs/mcp-python-sdk:wj/DI-3218-lowlevel-disconnect-debugCopy head branch name to clipboard