Add method to return undecided packages (#37)

This is used in uv for logging

src/internal/partial_solution.rs

@@ -257,6 +257,21 @@ impl<DP: DependencyProvider> PartialSolution<DP> {
         self.next_global_index += 1;
     }
 
+    /// The list of package that have not been selected after the last prioritization.
+    ///
+    /// This list gets updated by [`Self::pick_highest_priority_pkg`] and cleared by backtracking.
+    #[allow(clippy::type_complexity)]
+    pub fn undecided_packages(
+        &self,
+    ) -> impl Iterator<
+        Item = (
+            &Id<DP::P>,
+            &(<DP as DependencyProvider>::Priority, Reverse<u32>),
+        ),
+    > {
+        self.prioritized_potential_packages.iter()
+    }
+
     /// Add a derivation.
     pub(crate) fn add_derivation(
         &mut self,