Replace httpx and httpx-sse with httpx2 (#2972)

Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com>

tests/client/test_transport_stream_cleanup.py

@@ -16,7 +16,7 @@ import sys
 from collections.abc import Iterator
 from contextlib import contextmanager
 
-import httpx
+import httpx2
 import pytest
 
 from mcp.client.sse import sse_client
@@ -64,7 +64,7 @@ async def test_sse_client_closes_all_streams_on_connection_error(free_tcp_port:
     closed in the finally block.
     """
     with _assert_no_memory_stream_leak():
-        with pytest.raises(httpx.ConnectError):
+        with pytest.raises(httpx2.ConnectError):
             async with sse_client(f"http://127.0.0.1:{free_tcp_port}/sse"):
                 pytest.fail("should not reach here")  # pragma: no cover
 
@@ -76,18 +76,18 @@ async def test_sse_client_closes_all_streams_on_http_error() -> None:
     ExceptionGroup) with nothing to leak — the task group is never entered.
     """
 
-    def return_403(request: httpx.Request) -> httpx.Response:
-        return httpx.Response(403)
+    def return_403(request: httpx2.Request) -> httpx2.Response:
+        return httpx2.Response(403)
 
     def mock_factory(
         headers: dict[str, str] | None = None,
-        timeout: httpx.Timeout | None = None,
-        auth: httpx.Auth | None = None,
-    ) -> httpx.AsyncClient:
-        return httpx.AsyncClient(transport=httpx.MockTransport(return_403))
+        timeout: httpx2.Timeout | None = None,
+        auth: httpx2.Auth | None = None,
+    ) -> httpx2.AsyncClient:
+        return httpx2.AsyncClient(transport=httpx2.MockTransport(return_403))
 
     with _assert_no_memory_stream_leak():
-        with pytest.raises(httpx.HTTPStatusError):
+        with pytest.raises(httpx2.HTTPStatusError):
             async with sse_client("http://test/sse", httpx_client_factory=mock_factory):
                 pytest.fail("should not reach here")  # pragma: no cover