Roll Observatory packages and add a roll script

packages/quiver/lib/src/iterables/count.dart

 // Copyright 2013 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,
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   _CountIterator(num this._start, this._step);
 
   num get current => _current;
 
   bool moveNext() {
     _current = (_current == null) ? _start : _current + _step;
     return true;
   }
 }