fix: handle ClosedResourceError when logging errors to disconnected clients

Wrap send_log_message() in _handle_message's exception handler with a
try/except for ClosedResourceError and BrokenResourceError. When a client
disconnects during request processing, the server catches the stream
exception but then crashes trying to send the error log back through the
already-closed write stream.

Closes #2064

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: g97iulio1609

src/mcp/server/lowlevel/server.py

@@ -417,11 +417,14 @@ async def _handle_message(
                         )
                 case Exception():
                     logger.error(f"Received exception from stream: {message}")
-                    await session.send_log_message(
-                        level="error",
-                        data="Internal Server Error",
-                        logger="mcp.server.exception_handler",
-                    )
+                    try:
+                        await session.send_log_message(
+                            level="error",
+                            data="Internal Server Error",
+                            logger="mcp.server.exception_handler",
+                        )
+                    except (anyio.ClosedResourceError, anyio.BrokenResourceError):
+                        logger.debug("Could not send error log: client already disconnected")
                     if raise_exceptions:
                         raise message
                 case _: