feat/objbench:

### Add Metrics for Indexing and Conversion in `access_layer.rs` and `writer.rs`

 - **Enhancements in `access_layer.rs`:**
   - Added new metrics `convert` and `index` to the `Metrics` struct to track conversion and indexing durations.

 - **Updates in `writer.rs`:**
   - Implemented tracking of indexing duration by measuring the time taken for `update` in the indexer.
   - Added measurement of conversion duration for `convert_batch` to enhance performance monitoring.

Signed-off-by: Lei, HUANG <mrsatangel@gmail.com>

src/mito2/src/access_layer.rs

@@ -47,7 +47,8 @@ pub type SstInfoArray = SmallVec<[SstInfo; 2]>;
 pub struct Metrics {
     pub read: Duration,
     pub write: Duration,
-
+    pub convert: Duration,
+    pub index: Duration,
     pub close: Duration,
 }
 

src/mito2/src/sst/parquet/writer.rs

@@ -172,7 +172,9 @@ where
             match res {
                 Ok(mut batch) => {
                     stats.update(&batch);
+                    let index_start = Instant::now();
                     self.get_or_create_indexer().await.update(&mut batch).await;
+                    metrics.index += index_start.elapsed();
                 }
                 Err(e) => {
                     self.get_or_create_indexer().await.abort().await;
@@ -250,7 +252,9 @@ where
         };
         metrics.read += read_start.elapsed();
 
+        let convert_start = Instant::now();
         let arrow_batch = write_format.convert_batch(&batch)?;
+        metrics.convert += convert_start.elapsed();
 
         let write_start = Instant::now();
         self.maybe_init_writer(write_format.arrow_schema(), opts)