feat: Add backwards compatibility for StreamableHTTPTransport parameters

Keep constructor parameters (headers, timeout, sse_read_timeout, auth)
for backwards compatibility, but mark them as deprecated and ignore them.

The transport now reads all configuration from the httpx.AsyncClient
passed to request methods. These parameters are kept to avoid breaking
existing code that might instantiate the transport directly.

Author: felixweinberger

src/mcp/client/streamable_http.py

@@ -74,11 +74,22 @@ class RequestContext:
 class StreamableHTTPTransport:
     """StreamableHTTP client transport implementation."""
 
-    def __init__(self, url: str) -> None:
+    def __init__(
+        self,
+        url: str,
+        headers: dict[str, str] | None = None,
+        timeout: float | timedelta = 30,
+        sse_read_timeout: float | timedelta = 60 * 5,
+        auth: httpx.Auth | None = None,
+    ) -> None:
         """Initialize the StreamableHTTP transport.
 
         Args:
             url: The endpoint URL.
+            headers: DEPRECATED - Ignored. Configure headers on the httpx.AsyncClient instead.
+            timeout: DEPRECATED - Ignored. Configure timeout on the httpx.AsyncClient instead.
+            sse_read_timeout: DEPRECATED - Ignored. Configure read timeout on the httpx.AsyncClient instead.
+            auth: DEPRECATED - Ignored. Configure auth on the httpx.AsyncClient instead.
         """
         self.url = url
         self.session_id = None