Discrete-time variables are forced to `Float64`

[baggepinnen]

The example below creates a discrete-time system with a boolean discrete-time variable, it fails with

julia> prob = DiscreteProblem(sys, [], (0,10))
ERROR: MethodError: no method matching !(::Float64)

function Model(; name)
    @variables begin
        x(t)::Bool = true
    end
    equations = [
        x(k) ~ !x(k-1)
    ]
    DiscreteSystem(equations, t; name)
end

@mtkbuild sys = Model()
prob = DiscreteProblem(sys, [], (0,10))
sol = solve(prob, FunctionMap())
x = sol[sys.x(k+1)]
@test eltype(x) <: Bool