nix: trim the integration test VM toward a tiny profile

Drop doc generation and timesyncd in the check VM — it only needs to boot,
run docker, and exec one test binary. Boot is dominated by dockerd init
(functional); this shaves the avoidable NixOS userspace. microvm.nix is noted
as a larger follow-up since it still needs a full docker daemon + nested KVM.

Author: kradalby

nix/tests/integration.nix

@@ -74,6 +74,16 @@ in
     # /CablePull) and intermittent container-startup flakes. Keep it off them.
     networking.dhcpcd.denyInterfaces = [ "veth*" "br-*" "docker*" ];
 
+    # Trim the guest toward a tiny profile: this VM only needs to boot, run
+    # docker, and exec one test binary. Boot is ~20s and dominated by dockerd
+    # init (functional, can't trim) plus default NixOS userspace; dropping doc
+    # generation and unused services shaves the avoidable part. (A microvm.nix
+    # guest would go further but still needs a full docker daemon + nested KVM,
+    # so it is a larger follow-up than this profile for a small boot win against
+    # the ~2-3 min image-load + test runtime.)
+    documentation.enable = false;
+    services.timesyncd.enable = false;
+
     # Sized for the full version matrix (a test can spawn 12+ tailscale
     # containers + headscale + the runner) while still fitting a standard
     # 4-core/16 GB GitHub runner. Disk-backed docker (not tmpfs) keeps RAM