reconsider GetStatistics effects

[banesullivan]

GetStatistics() with GDAL currently uses bApproxOK=True and bForce=True. We should evaluate if these are the best choices (see https://gdal.org/doxygen/classGDALRasterBand.html#a6aa58b6f0a0c17722b9bf763a96ff069)

large_image/sources/gdal/large_image_source_gdal/__init__.py

Line 582 in 2bcc4f0

stats = band.GetStatistics(True, True)

This is yielding different results than rasterio's default statistics() methods and gives the wrong max value for rgb_geotiff.tiff specifically which is set in the unit tests:

large_image/test/test_source_gdal.py

Line 70 in 2bcc4f0

assert tileMetadata['bands'][2]['max'] == 212.0

The true max value for this file is 240, not 212. Setting bApproxOK=False gives the correct value of 240.

I think we probably want to dynamically choose bApproxOK based on the overall size of the image. If its smaller than some threshold, use bApproxOK=False to get the true value and if it's over some threshold, use bApproxOK=True for efficiency.