fix: also require carrier for parallel builds

`purrr::in_parallel()` uses `carrier::crate()` to serialize worker
closures and raises an undeclared-dependency error partway through if
carrier isn't installed. Add carrier to Suggests and to the
`rlang::check_installed()` pre-flight so the requirement is surfaced
up-front with pkgdown's own error path.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

Author: billdenney

DESCRIPTION

@@ -46,6 +46,7 @@ Imports:
     xml2 (>= 1.3.1),
     yaml (>= 2.3.9)
 Suggests:
+    carrier,
     covr,
     diffviewer,
     evaluate (>= 0.24.0),

R/build-articles.R

@@ -232,7 +232,7 @@ build_articles <- function(
       quiet = quiet
     ))
   } else {
-    rlang::check_installed("mirai")
+    rlang::check_installed(c("mirai", "carrier"))
     mirai::daemons(n_cores)
     withr::defer(mirai::daemons(0))
     unwrap_purrr_error(purrr::walk(

R/build-quarto-articles.R

@@ -72,7 +72,7 @@ build_quarto_articles <- function(
       output_dir = output_dir
     ))
   } else {
-    rlang::check_installed("mirai")
+    rlang::check_installed(c("mirai", "carrier"))
     mirai::daemons(n_cores)
     withr::defer(mirai::daemons(0))
     unwrap_purrr_error(purrr::walk2(