data frame printing and overwriting methods for greta arrays

A few things:

- When you put a greta array inside a tibble, it has a funky print method
- a greta array inside a tibble can be pulled out and is still a greta array
- a greta array in a data.frame prints NA
- a greta array inside data.frame gets its class stripped off of it

``` r
library(tibble)
library(greta)
#>
#> Attaching package: 'greta'
#> The following objects are masked from 'package:stats':
#>
#> binomial, cov2cor, poisson
#> The following objects are masked from 'package:base':
#>
#> %*%, apply, backsolve, beta, chol2inv, colMeans, colSums, diag,
#> eigen, forwardsolve, gamma, identity, rowMeans, rowSums, sweep,
#> tapply
ihr_car_ratio <- greta::uniform(0,1)
#> ℹ Initialising python and checking dependencies, this may take a moment.
#> ✔ Initialising python and checking dependencies ... done!
#>

ihr_car_ratio
#> greta array (variable following a uniform distribution)
#>
#> [,1]
#> [1,] ?

greta_tbl <- tibble(
x = 1:5,
car_ratio = ihr_car_ratio
)

greta_df <- data.frame(
x = 1:5,
car_ratio = ihr_car_ratio
)

greta_tbl
#> # A tibble: 5 × 2
#> x car_ratio[,1]
#>
#> 1 1 NA
#> 2 2 car_ratio[,1]
#> 3 3
#> 4 4 NA
#> 5 5 car_ratio[,1]
greta_df
#> x car_ratio
#> 1 1 NA
#> 2 2 NA
#> 3 3 NA
#> 4 4 NA
#> 5 5 NA

greta_tbl$car_ratio
#> greta array (variable following a uniform distribution)
#>
#> [,1]
#> [1,] ?
greta_df$car_ratio
#> [1] NA NA NA NA NA
```

^{Created on 2024-04-30 with [reprex v2.1.0](https://reprex.tidyverse.org)}

Session info

``` r
sessioninfo::session_info()
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#>
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#> ──────────────────────────────────────────────────────────────────────────────
```