021 store f64 scalar columns

// 690_020 TIER 1 spelling pin: scalar column widening — a singleton store
// with f64 columns (kernel:shape's green f64 precedent, 390_001, applied
// to the store cell). Uniform-type stores only this slice; mixed types
// are walled loudly. Promoted from residue pin 690_020.

~import std/io
~import std/store

~std/store:create(temps) { celsius: 21.5[f64] }

~std/store:watch(temps)
! celsius c |> std/io:print.ln("{{ c:f }} C")

~std/store:stored { temps.celsius: temps.celsius + 1.5 }