Stats propagation through compression

[gatesn]

The stats of a compressed array should equal the stats of the uncompressed array.

Further, the stats from the compressed array can be used to populate the stats of compressed internals. e.g. the internal array of ZigZag encoding should zigzag_encode the min/max from the original array to compute a potential new max.

[gatesn]

In ctx.compress, we could call stats.update on the result array before returning

[gatesn]

Closed in favour of #291