Provide some mechanism for reporting the size of a RasterSource.

[metasim]

There are cases where before (and after?) reading a RasterSource one would want to know how big it is (dimensions as well as footprint?).

[metasim]

This needs more clarification. Outside of a dataframe, RasterSource has rows and cols (and I think size) methods. Once in a dataframe, it's been tiled and some of that is lost and has to be reconstructed through aggregates.

One potentiality is to have the option of adding to each post-tiling dataframe a column that is something like rastersource_metadata, containing stuff including the original size.