[POC]: Add statistics to xdem.coreg.BlockwiseCoreg.stats()

[quinto-clara]

Description :

When XDEM performs a Blockwise coregistration, the output DataFrame xdem.coreg.BlockwiseCoreg.stats() contains : inliers, x-y-z_offset, x-y-z_center, median and nmad of elevation differences after coregistration. We would like to add more statistics to the DataFrame.

New statistics and values for each subdivision :

General :

• Row number
• Column number
• Percentage of valid points
• Number of pixels

For the elevation differences after coregistration :

• Mean
• Maximum
• Minimum
• Standard deviation
• Root mean squared error
• 90th percentile
• Sum
• Sum squared