feat: add public accessors for count plan construction

rust/lance/src/dataset/fragment.rs

@@ -1347,7 +1347,7 @@ impl FileFragment {
     }
 
     /// Get the deletion vector for this fragment, using the cache if available.
-    pub(crate) async fn get_deletion_vector(&self) -> Result<Option<Arc<DeletionVector>>> {
+    pub async fn get_deletion_vector(&self) -> Result<Option<Arc<DeletionVector>>> {
         let Some(deletion_file) = self.metadata.deletion_file.as_ref() else {
             return Ok(None);
         };

rust/lance/src/dataset/scanner.rs

@@ -1473,7 +1473,7 @@ impl Scanner {
         Ok(concat_batches(&schema, &batches)?)
     }
 
-    fn create_count_plan(&self) -> BoxFuture<'_, Result<Arc<dyn ExecutionPlan>>> {
+    pub fn create_count_plan(&self) -> BoxFuture<'_, Result<Arc<dyn ExecutionPlan>>> {
         // Future intentionally boxed here to avoid large futures on the stack
         async move {
             if self.projection_plan.physical_projection.is_empty() {

rust/lance/src/io/exec/filtered_read.rs

@@ -66,6 +66,17 @@ pub struct EvaluatedIndex {
 }
 
 impl EvaluatedIndex {
+    /// Get the row id mask representing which rows matched the index filter.
+    pub fn index_result(&self) -> &IndexExprResult {
+        &self.index_result
+    }
+
+    /// Get a reference to the applicable fragments bitmap, containing the set of fragment IDs
+    /// implicated by the filter.
+    pub fn applicable_fragments(&self) -> &RoaringBitmap {
+        &self.applicable_fragments
+    }
+
     pub fn try_from_arrow(batch: &RecordBatch) -> Result<Self> {
         if batch.num_rows() != 2 {
             return Err(Error::InvalidInput {