Allow access to internal Utils for debugging purposes and improve usage stats.

Is your feature request related to a problem? Please describe. My team is considering migrating from Picasso to Coil. We have had an internal debugging tool with Picasso that allows us to view stats of the Picasso instance, using the Picasso StatsSnapshot object. We would like to keep that functionality, and it looks like some of the same logic is already in this library.

Describe the solution you’d like Cache data appears to be already present in coil.util.Utils but it is marked as internal. Not all of the stats that we use are tracked however. It would useful to have similar snapshot functionality with Coil.

Additional context Here are the stats accessible in StatsSnapshot

  public final int maxSize;
  public final int size;
  public final long cacheHits;
  public final long cacheMisses;
  public final long totalDownloadSize;
  public final long totalOriginalBitmapSize;
  public final long totalTransformedBitmapSize;
  public final long averageDownloadSize;
  public final long averageOriginalBitmapSize;
  public final long averageTransformedBitmapSize;
  public final int downloadCount;
  public final int originalBitmapCount;
  public final int transformedBitmapCount;

[colinrtwhite]

Closing this as EventListener can be used to build stats tracking functionality.

[colinrtwhite]

The approach would be similar to Picasso 3 - provide an EventListener implementation that tracks the stats.