Default RubricMiddleware.max_iterations, shown without importing the SDK.
Hardcoded rather than read from deepagents.middleware.rubric.RubricMiddleware
because this module is dependency-free and importing the SDK for a display
string would violate the startup-performance rule (see AGENTS.md). This is a
hand-maintained duplicate that can rot if the SDK bumps its default, so
test_reliable_rubric.py::TestReliableRubricMiddleware::test_displayed_max_iterations_default_matches_sdk
is the drift guard that fails when the two diverge.
