Sandbox libxml2 and switch clang to zstd compression

When trying to execute clang on a very very fresh Debian image, it can't
find libxml2.  Sandbox that too.

While we are here, zstd images extract faster than xz.  Switch over.

Change-Id: Ia196ae49223b488f5eabe28b67e6f274b3072795
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/debian/packages.bzl b/debian/packages.bzl
index d39f613..97d6355 100644
--- a/debian/packages.bzl
+++ b/debian/packages.bzl
@@ -32,7 +32,7 @@
 #    output from the previous step.
 # 4. Follow steps 2., 5., and 6. from "adding new packages".
 
-def download_packages(name, packages, excludes = [], force_includes = [], force_excludes = [], target_compatible_with = None, release = "bullseye"):
+def download_packages(name, packages, excludes = [], force_includes = [], force_excludes = [], target_compatible_with = None, release = "bookworm"):
     """Downloads a set of packages as well as their dependencies.
 
     You can also specify excludes in case some of the dependencies are meta