gh-157429: Make test_detach_materialized_dict_no_memory deterministic - #157444

Add _testcapi.call_with_nomemory(start, stop, func, /, *args) which arms the allocation failure as set_nomemory(), calls func(*args) and removes the memory hooks, without executing any bytecode in between. So the work pending at the eval breaker (GC, deferred frees and refcount merges on free-threading builds) cannot run inside the failure window and consume the failing allocation.

The test now drops the last reference from C with lst.clear passed to this helper, so the first allocation in the window is always the one in detach_dict_from_object(). It only accepts the unraisable exception reported while clearing the managed dict, and its failure message lists what was actually seen for each n. Since nothing but the deallocation can run while the hooks are armed, the test no longer needs a subprocess.

Keeping ex.unraisable alive across iterations leaked references once the test ran in-process (gh-157443), so only exc_type and err_msg are taken out of the with block.

• Issue: test_class.test_detach_materialized_dict_no_memory() fails randomly on the Free Threading macOS CI #157429