cancelDistanceResolution

R74 fix: synchronous cancel for "the user just selected a row". Flipping cancelled stops the per-row routing loop from issuing further requestRouteForDistance calls AND drops the in-flight worker out of its short-poll latch.await within ~200 ms (see resolveDistancesAsync). That way the engine's JNI routing mutex is freed (or nearly so) by the time the user's selected requestRoute(...) is issued, instead of contending for up to ~8 s with whichever row was mid-flight at the moment of the tap. Must be called BEFORE dismissAllowingStateLoss() on row tap and BEFORE navigateClosestLocationClicked(...) on "Navigate Closest" — i.e. before the selected route's own request is issued.