[FEA] Enable option in `build.sh` to build self-contained tarball

We now have a script for CI to build a standalone tarball of cuvs here. However, this script assumes it's being run in a CI environment (complete with functions for rapids-logger and appropriate env vars set).

We would like to enable a simple way for users to build the tarballs themselves using a method like:

build.sh libcuvs --install build/libcuvs_c --rapids-static
tar czvf libcuvs_c.tar.gz build/libcuvs_c

Even better, if we could have a simple command like this:

build.sh standalone

Which could build libcuvs automatically, then construct the tarball and put it in the build/ directory.

Start with build.sh and trace the CI-only functions, rapids-logger calls, and required environment variables. Define the standalone entry point or option so it builds libcuvs, creates the self-contained tarball, and places it in build/; verify the documented command works outside CI.