Create a statistic to count the number of values within specified bounds

[katmatson]

Add support to compute a 'bounded_count' statistic based on a 'bounds' tuple. This will count the number of vectors with a value for the specified property that is within the provided bounds.

For example, in the lake change dataset, to add statistics to count the number of expanding and shrinking lakes within each tile, the viz-staging config would include:

statistics = [
    {
      "name": "growing_lakes", 
      "property": "ChangeRateNet_myr-1", 
      "aggregation_method": "bounded_count", 
      "resampling_method": "sum",  
      "bounds": (0, None)
      # ... other standard fields related to display
    },
    {
      "name": "shrinking_lakes", 
      "property": "ChangeRateNet_myr-1", 
      "aggregation_method": "bounded_count", 
      "resampling_method": "sum",  
      "bounds": (None, 0)
      # ... other standard fields related to display
    },
]

Together with PermafrostDiscoveryGateway/viz-staging#57, this addresses issue #33