Ensure dose and response are numeric about dreamer

[rich-payne]

Fixed as of f0fb639:

devtools::load_all()
#> ℹ Loading dreamer
data <- data.frame(dose = factor(1:2), response = 11:12)
dreamer_mcmc(
    data,
    mod = model_independent(
        mu_b1 = rep(0, 2),
        sigma_b1 = rep(1, 2),
        doses = c(1, 2),
        shape = 1,
        rate = .01
    )
)
#> Error in `check_data()` at dreamer/R/dreamer.R:62:2:
#> ! Column "dose" in data must be numeric.

^{Created on 2022-07-13 by the reprex package (v2.0.1)}