publish:
* encrypt and encode times are cumulative, not just current-segment
retrieve:
* same for decrypt and decode times
* update "current status" to include segment number
* set status to Finished/Failed when download is complete
* set progress to 1.0 when complete
More improvements to consider:
* progress is currently 0% or 100%: should calculate how many segments are
involved (remembering retrieve can be less than the whole file) and set it
to a fraction
* "fetch" time is fuzzy: what we want is to know how much of the delay is not
our own fault, but since we do decode/decrypt work while waiting for more
shares, it's not straightforward
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