Use ALTREP safe operations

For instance, viewing a tibble unnecessarily evaluates the sequences:

library(vecvec)
x <- tibble::tibble(x = vecvec(seq_len(1e6)), y = seq_len(1e6))
pryr::object_size(x$x)
#> 32.90 kB
pryr::object_size(x$y)
#> 680 B
x
#> # A tibble: 1,000,000 × 2
#>    x           y
#>    <int*>  <int>
#>  1       1     1
#>  2       2     2
#>  3       3     3
#>  4       4     4
#>  5       5     5
#>  6       6     6
#>  7       7     7
#>  8       8     8
#>  9       9     9
#> 10      10    10
#> # ℹ 999,990 more rows
pryr::object_size(x$x)
#> 4.03 MB
pryr::object_size(x$y)
#> 680 B

^{Created on 2026-04-10 with reprex v2.1.1}

Start by running the reproducible R example in the issue and inspect the ALTREP-related vector operations used by vecvec. Determine which operation during tibble viewing materializes x, then verify that viewing the tibble leaves the sequence compact.