feat(tvix/cli): add toplevel progress span

This gives some better feedback something is going on, gives a (named)
root for all the progress children we're drawing, and also counts the
time we are in eval.

Change-Id: Ibe81dcebf0a2b59bb0680da62e206eb5270f9d3c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11798
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: aspen <root@gws.fyi>

tvix/Cargo.nix

@@ -13305,6 +13305,10 @@ rec {
             name = "tracing";
             packageId = "tracing";
           }
+          {
+            name = "tracing-indicatif";
+            packageId = "tracing-indicatif";
+          }
           {
             name = "tvix-build";
             packageId = "tvix-build";