More robust use of isapprox when checking time steps in tdvp (#107)

Author: ultimatile

src/solvers/tdvp.jl

@@ -31,7 +31,7 @@ end
 function time_step_and_nsteps(t, time_step, nsteps::Nothing)
   nsteps_float = t / time_step
   nsteps_rounded = round(nsteps_float)
-  if abs(nsteps_float - nsteps_rounded) ≉ 0
+  if nsteps_float ≉ nsteps_rounded
     return error("`t / time_step = $t / $time_step = $(t / time_step)` must be an integer.")
   end
   return time_step, Int(nsteps_rounded)