median implementation is slow about rolling

[ajcr]

Many thanks for this interesting observation and links, @belm0.

List + bisect sounds like a good first alternative to the skiplist and shouldn't be too difficult to implement (?).

Perhaps if there's demand for increased performance at the window sizes you mention, SortedList can be used. I quite like the fact that rolling has no third-party dependencies yet, but there's no requirement to keep it this way if there's a good reason to use one.