fix(gateway): align ChoreographerHelpers._briefing_for stub with impl

The spec-2 change added `include_ac_coverage` to Choreographer._briefing_for
(_impl.py) but not to the typed stub in _protocol.py that the role mixins
inherit for static analysis. The composed Choreographer (board/doc/qa mixins +
_LegacyChoreographer) then had two incompatible _briefing_for signatures in its
MRO — caught by full `mypy roboco/ tests/` (not by a per-file check). Add the
same keyword to the stub. mypy clean at CI scope (648 files).

roboco/services/gateway/choreographer/_protocol.py

@@ -59,6 +59,7 @@ class ChoreographerHelpers:
         task_id: UUID | None,
         *,
         task: Any | None = None,
+        include_ac_coverage: bool = False,
     ) -> dict[str, Any]:
         raise NotImplementedError