[roll] Roll fuchsia [virtualization] Use fpromise in BlockDispatcher

Refactor BlockDispatcher to use fpromise::promise instead of callbacks
to manage IO operations.

Original-Bug: 93355
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/650706
Original-Revision: 0815eb73f8217865ba514118676cd97494f80850
GitOrigin-RevId: 56e09da909c264f9ec7b1fcc95c8a6ea772367c5
Change-Id: I3e97389012ddc5785dc6fbd2c7393c526bb81c2f
diff --git a/stem b/stem
index 5ee2d12..998eab2 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
              githooks=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="e7dab2daa4a52078e123de96a3c36960356c6ba8"/>
+             revision="0815eb73f8217865ba514118676cd97494f80850"/>
   </projects>
   <hooks>
     <hook name="install-environment"