speed up ensure_parsnip_format()

[simonpcouch]

A helper that gets a good bit of traffic at predict().

With main dev:

library(parsnip)

lm_fit <- fit(linear_reg(), mpg ~ ., mtcars)

bench::mark(old = predict(lm_fit, mtcars))
#> # A tibble: 1 × 6
#>   expression      min   median `itr/sec` mem_alloc `gc/sec`
#>   <bch:expr> <bch:tm> <bch:tm>     <dbl> <bch:byt>    <dbl>
#> 1 old           619µs    654µs     1476.    1.08MB     35.9

With this PR:

bench::mark(new = predict(lm_fit, mtcars))
#> # A tibble: 1 × 6
#>   expression      min   median `itr/sec` mem_alloc `gc/sec`
#>   <bch:expr> <bch:tm> <bch:tm>     <dbl> <bch:byt>    <dbl>
#> 1 new           389µs    404µs     2419.     599KB     40.3

^{Created on 2023-04-02 with reprex v2.0.2}

[hfrick]

🏇

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