set_engine() removes quantile levels

[topepo]

library(tidymodels)

qnt_lvls <- (1:3) / 4

linear_reg() |> 
  set_engine("quantreg") |> 
  set_mode("quantile regression", quantile_levels = qnt_lvls)
#> Linear Regression Model Specification (quantile regression)
#> 
#> Computational engine: quantreg
#> Quantile levels: 0.25, 0.5, and 0.75.

linear_reg() |> 
  set_mode("quantile regression", quantile_levels = qnt_lvls) |> 
  set_engine("quantreg")
#> Linear Regression Model Specification (quantile regression)
#> 
#> Computational engine: quantreg
#> Quantile levels: .

^{Created on 2025-11-14 with reprex v2.1.1}

We should create a constructor function for model specifications to avoid this issue in the future.