`build_readme()` extremely slow due to `pak::local_install_deps()` installing full dependency tree in temp

[BjarkeHautop]

After the release of devtools 2.5.0, build_readme() has become very slow for packages with moderate dependency trees.

build_readme() installs the package in a temporary directory

devtools/R/install.R

Line 256 in ee2ae31

withr::local_temp_libpaths(.local_envir = env)

Because of this, pak::local_install_deps() installs the entire dependency tree in temp, even if all dependencies are already installed in the user's normal libraries. This is intended pak behavior, see
https://github.com/r-lib/pak/blob/63d646be4d2d59c29ea02cd99a68fb5b2c4164fd/R/package.R#L15-L17
(and is different from how remotes does it).

For packages with heavier dependency trees, this can add several minutes to build_readme(). E.g. for a package I maintain, on my machine it takes ~7 minutes to complete the pak::local_install_deps() call (~90 seconds if using Posit Package Manager binaries).

While this is happening, no useful progress information is printed, even with quiet = FALSE. The user sees no indication that a large dependency installation is occurring.