refactor: use snake case instead of camel case in types (#1894)

tests/client/test_list_roots_callback.py

@@ -45,7 +45,7 @@ async def test_list_roots_callback():
     async with create_session(server._mcp_server, list_roots_callback=list_roots_callback) as client_session:
         # Make a request to trigger sampling callback
         result = await client_session.call_tool("test_list_roots", {"message": "test message"})
-        assert result.isError is False
+        assert result.is_error is False
         assert isinstance(result.content[0], TextContent)
         assert result.content[0].text == "true"
 
@@ -53,6 +53,6 @@ async def test_list_roots_callback():
     async with create_session(server._mcp_server) as client_session:
         # Make a request to trigger sampling callback
         result = await client_session.call_tool("test_list_roots", {"message": "test message"})
-        assert result.isError is True
+        assert result.is_error is True
         assert isinstance(result.content[0], TextContent)
         assert result.content[0].text == "Error executing tool test_list_roots: List roots not supported"