[roll] Roll fuchsia [diagnostics] Improve reader,hierarchy and testing crates documentaiton

These docs were pretty complete, but added some minor stuff.

Original-Fixed: 60782
Tested: rustdoc preview

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/462759
Original-Revision: 4906cd45c7b35c2a3b759438ad8d5267f29152bb
GitOrigin-RevId: ab317bcf42bcbb6fabf36d93b656bf828a937fba
Change-Id: I6c215016dcecc1eb22e4c109e52e44deaaf8a98b
diff --git a/stem b/stem
index 760fecb..cb63fd2 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
              githooks=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="0eeec755745a07fb86b8a084415db09fdcedf1aa"/>
+             revision="4906cd45c7b35c2a3b759438ad8d5267f29152bb"/>
   </projects>
   <hooks>
     <hook name="install-fx"