+str #15223 `timed` extra combinators for Duct
Note: not too happy about duplication of impl, but is required due to
the Flow and Duct not sharing any types (could use structural, not going there though).

Resolves #15223
Merge pull request #15225 from ktoso/wip-timed-duct-ktoso

+str Timed ops for Duct[I, O]