Roll Observatory packages and add a roll script

quiver/lib/src/time/duration_unit_constants.dart

-// Copyright 2014 Google Inc. All Rights Reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-part of quiver.time;
-
-const Duration aMicrosecond = const Duration(microseconds: 1);
-const Duration aMillisecond = const Duration(milliseconds: 1);
-const Duration aSecond = const Duration(seconds: 1);
-const Duration aMinute = const Duration(minutes: 1);
-const Duration anHour = const Duration(hours: 1);
-const Duration aDay = const Duration(days: 1);
-const Duration aWeek = const Duration(days: 7);