revert: use try/finally for sse and streamable_http stream cleanup

The async with form triggers coverage.py false-positive branch arcs
on Python 3.14 — nested multi-CM async with creates WITH_EXCEPT_START
handlers whose POP_JUMP_IF_TRUE branches (did __aexit__ suppress?)
get attributed to inner async with lines via the exception table.
Memory stream __aexit__ never suppresses, so those arcs are
unreachable, but coverage.py's static analysis expects them.

try/finally has no suppression branch (it's unconditional RERAISE),
so it sidesteps the issue entirely. Keeping the explicit aclose()
chain for these two files; websocket.py stays on the merged
async with form since its single-level nesting is clean on all
tested Python versions (3.10-3.14).

Author: maxisbey

src/mcp/client/sse.py

@@ -61,7 +61,7 @@ async def sse_client(
     write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
 
     async with anyio.create_task_group() as tg:
-        async with read_stream_writer, read_stream, write_stream, write_stream_reader:
+        try:
             logger.debug(f"Connecting to SSE endpoint: {remove_request_params(url)}")
             async with httpx_client_factory(
                 headers=headers, auth=auth, timeout=httpx.Timeout(timeout, read=sse_read_timeout)
@@ -157,3 +157,8 @@ async def post_writer(endpoint_url: str):
                         yield read_stream, write_stream
                     finally:
                         tg.cancel_scope.cancel()
+        finally:
+            await read_stream_writer.aclose()
+            await write_stream.aclose()
+            await read_stream.aclose()
+            await write_stream_reader.aclose()

src/mcp/client/streamable_http.py

@@ -547,7 +547,7 @@ async def streamable_http_client(
     transport = StreamableHTTPTransport(url)
 
     async with anyio.create_task_group() as tg:
-        async with read_stream_writer, read_stream, write_stream, write_stream_reader:
+        try:
             logger.debug(f"Connecting to StreamableHTTP endpoint: {url}")
 
             async with contextlib.AsyncExitStack() as stack:
@@ -574,3 +574,8 @@ def start_get_stream() -> None:
                     if transport.session_id and terminate_on_close:
                         await transport.terminate_session(client)
                     tg.cancel_scope.cancel()
+        finally:
+            await read_stream_writer.aclose()
+            await write_stream.aclose()
+            await read_stream.aclose()
+            await write_stream_reader.aclose()