value is stripped of its class in comparison validation functions

[yjunechoe]

Discovered while investigating #536. Reprex:

agent <- data.frame(date = as.Date(1)) |>
  create_agent() |> 
  col_vals_lt(date, Sys.Date()) |> 
  interrogate()

In the example above, the user might expect col_vals_lt() to compare the column to the value of Sys.Date(), a date object. Instead, I found that it's constructing the expression date < 19881 inside tbl_val_comparison().

I tracked this down to get_values_at_idx() (which is called by interrogate_comparison()). The class stripping happens due to the way get_values_at_idx() is written:

pointblank:::get_values_at_idx
#> function (agent, idx) 
#> {
#>     agent$validation_set[[idx, "values"]] %>% unlist(recursive = FALSE)
#> }
#> <bytecode: 0x0000026ee1918a60>
#> <environment: namespace:pointblank>

It seems that unlist() is stripping the value of its class:

agent$validation_set[[1, "values"]]
#> [[1]]
#> [1] "2024-06-07"

class(agent$validation_set[[1, "values"]][[1]])
#> [1] "Date"

agent$validation_set[[1, "values"]] |> unlist()
#> [1] 19881

As far as I can see this isn't producing any bugs on known behaviors, but I thought it'd be nice to try to preserve the class (this may be helpful in tackling #536). But I may also be missing something - please let me know!