Smooth should accept date/time axes #250
Description
This issue is a leftover from #223.
Currently the smooth requires the x to be continuous otherwise the computations don't work.
I've tried casting Dates as numeric, but got stuck on translating them back.
I couldn't translate them back to Dates, because fractional dates don't exist.
I couldn't translate them to Datetime because of some implementation detail.
I tried enlisting claude in solving this issue but we couldn't find a satisfactory solution at the time.
So this is a TODO issue mostly.