rust-repo: add a method to get a `Node` from a `Revision` to the `Repo`

This is going to be more and more useful as we start writing higher-level code

rust/hg-core/src/repo.rs

@@ -797,6 +797,12 b' impl Repo {'
             )?,
         })
     }
+
+    pub fn node(&self, rev: UncheckedRevision) -> Option<crate::Node> {
+        self.changelog()
+            .ok()
+            .and_then(|c| c.node_from_rev(rev).copied())
+    }
 }
 
 /// Lazily-initialized component of `Repo` with interior mutability