Improve checking of parameter inputs to parameters() and grid_*() functions

[hfrick]

Closes #422

This fixes most of what's laid out in the reprex from the issue (comments still refer to the old behavior). It doesn't add a better error for grid_*.default() since that's a separate issue (#429).

library(dials)
#> Loading required package: scales

# constructor -----------------------------

# no input
# should error (for now) but has a cli error that shouldn't show
parameters() 
#> Error in `parameters()`:
#> ! No input provided. Please supply at least one parameter object.

# dispatch from param object

## should error but doesn't tell you which one is wrong
parameters(mtry(), "min_n") 
#> Error in `parameters()`:
#> ! `Argument 2` must be a <param> object, not the string "min_n".

# dispatch from list

## should error but doesn't tell you which one is wrong
parameters(list(mtry(), "min_n"))
#> Error in `parameters()`:
#> ! `Argument 2` must be a <param> object, not the string "min_n".


# grid functions ----------------------

# should this error or just return an empty tibble?
# if it should error, it needs a better error message
grid_regular() 
#> Error in `UseMethod()`:
#> ! no applicable method for 'grid_regular' applied to an object of class "NULL"

# dispatch from param object

## fires from constructor, 
## thus doesn't tell you which one is wrong *and* 
## has the wrong call
grid_regular(penalty(), "min_n")
#> Error in `grid_regular()`:
#> ! `Argument 2` must be a <param> object without unknowns, not the string "min_n".

# dispatch from list

## fires from constructor, 
## thus doesn't tell you which one is wrong *and* 
## has the wrong call
grid_regular(list(mtry(), "min_n"))
#> Error in `grid_regular()`:
#> ✖ `mtry` must be a <param> object without unknowns.
#> ℹ See the `dials::finalize()` function.

^{Created on 2026-04-08 with reprex v2.1.1}

The formatting of "Argument 2" as code isn't exactly perfect but comes from stop_input_type() which I (currently) don't think is worth taking apart to customize.

I ran revdep checks and it flags tdarec but that's because it's pulling in the unexported check function...

check_param <- getFromNamespace("check_param", "dials")

https://github.com/tdaverse/tdarec/blob/1f60a200f2d67a607ea7c774d62d20ab2ebefef8/R/vpd-summarizers.R#L34

[hfrick]

Pulling out this commit description for more visibility:
validate_params() can be removed when the user-facing grid_max_entropy() and grid_latin_hypercube() are removed and make_max_entropy_grid() and make_latin_hypercube_grid() don't need validate_params() anymore