Avoid restricting the star-import surface; re-export via aliases

Review feedback: the module-level __all__ added previously would have
replaced Python's implicit star-import behavior and dropped previously
exported names (SessionMessageOrError, DEFAULT_RECONNECTION_DELAY_MS,
etc.) for any `from mcp.client.streamable_http import *` consumer. Drop
__all__ and mark the re-exports with redundant aliases instead, which is
additive only — the star-import surface is unchanged apart from the newly
exported names.

Refs #3238

Author: ProgrammerPlus1998

src/mcp/client/streamable_http.py

@@ -33,33 +33,14 @@
 from mcp.client._transport import TransportStreams
 from mcp.shared._compat import resync_tracer
 from mcp.shared._context_streams import ContextReceiveStream, ContextSendStream, create_context_streams
-from mcp.shared._httpx_utils import (
-    MCP_DEFAULT_SSE_READ_TIMEOUT,
-    MCP_DEFAULT_TIMEOUT,
-    McpHttpClientFactory,
-    create_mcp_http_client,
-)
+from mcp.shared._httpx_utils import MCP_DEFAULT_SSE_READ_TIMEOUT as MCP_DEFAULT_SSE_READ_TIMEOUT
+from mcp.shared._httpx_utils import MCP_DEFAULT_TIMEOUT as MCP_DEFAULT_TIMEOUT
+from mcp.shared._httpx_utils import McpHttpClientFactory as McpHttpClientFactory
+from mcp.shared._httpx_utils import create_mcp_http_client
 from mcp.shared.inbound import MCP_PROTOCOL_VERSION_HEADER
 from mcp.shared.jsonrpc_dispatcher import cancelled_request_id_from_params
 from mcp.shared.message import ClientMessageMetadata, SessionMessage
 
-__all__ = [
-    "LAST_EVENT_ID",
-    "MAX_RECONNECTION_ATTEMPTS",
-    "MCP_DEFAULT_SSE_READ_TIMEOUT",
-    "MCP_DEFAULT_TIMEOUT",
-    "MCP_SESSION_ID",
-    "McpHttpClientFactory",
-    "RequestContext",
-    "ResumptionError",
-    "StreamReader",
-    "StreamWriter",
-    "StreamableHTTPError",
-    "StreamableHTTPTransport",
-    "create_mcp_http_client",
-    "streamable_http_client",
-]
-
 logger = logging.getLogger(__name__)