feat: collection-modification broadcast

[wlsnmrk]

Added a general-purpose broadcast for all modifications to auto collections.

In some cases, a user will only want to know that a collection has been modified, without regard to what the modification was. (An example use case: saving a list of high scores to disk whenever the list is modified, whether that's adding a new score or replacing an old one.)

In such cases it is cumbersome to subscribe to all notifications, as the callbacks have different signatures. Currently, the user must do:

public void SubscribeToHighScoreChanges()
{
  _scoresBinding = HighScores.Bind();
  _scoresBinding.OnAdd(OnHighScoreAdded);
  _scoresBinding.OnRemove(OnHighScoreRemoved);
  _scoresBinding.OnUpdate(OnHighScoreUpdated);
  _scoresBinding.OnClear(OnHighScoresCleared);
}

public void OnHighScoreAdded(HighScore _) => SaveHighScores();
public void OnHighScoreRemoved(HighScore _) => SaveHighScores();
public void OnHighScoreUpdated(HighScore _, HighScore __) => SaveHighScores();
public void OnHighScoresCleared() => SaveHighScores();

public void SaveHighScores()
{
  // ...
}

(Granted, the OnClear() callback could be a direct call to SaveHighScores since the signature matches, and perhaps the Added/Removed callbacks could be condensed into one, but the structure of the code becomes less clear as these elisions are made.)

This PR adds a general-purpose modification callback to all auto-collections:

public void SubscribeToHighScoreChanges()
{
  _scoresBinding = HighScores.Bind();
  _scoresBinding.OnModify(SaveHighScores);
}

public void SaveHighScores()
{
  // ...
}

I've also updated some xmldocs comments to match comparable comments on other collections, updated a couple test names to be consistent, and updated the clear tests for AutoMap and AutoSet to verify that they only broadcast when the collection is non-empty (similar to the tests for AutoList).

[jolexxa]

💯