feat: add merge operation specs and partition progress bar

Added implementation specifications for the `merge` operation, detailing parallel partition processing, I/O paths, and kmer matrix aggregation across multiple indexes. Integrated an `indicatif` progress bar into the `rayon` parallel loop to monitor processing position, throughput, ETA, and recent partition duration.

src/obikpartitionner/src/partition.rs

@@ -219,19 +219,34 @@ impl KmerPartition {
         let n_threads = rayon::current_num_threads().max(1) as u64;
         let available_per_thread = available / n_threads;
 
+        let pb = ProgressBar::new(self.n_partitions as u64);
+        pb.set_style(
+            ProgressStyle::with_template(
+                "dereplicating [{bar:40}] {pos}/{len} ({percent}%)  {per_sec}  eta {eta}  {msg}",
+            )
+            .unwrap()
+            .progress_chars("█▌░"),
+        );
+
         let results: Vec<SKResult<()>> = (0..self.n_partitions)
             .into_par_iter()
             .map(|i| {
                 let dir = self.part_dir(i);
                 if !dir.exists() {
+                    pb.inc(1);
                     return Ok(());
                 }
                 let raw_path = dir.join(format!("raw.{SK_EXT}"));
+                let t = Instant::now();
                 let n_buckets = optimal_buckets(&raw_path, available_per_thread);
-                dereplicate_partition(&dir, level, n_buckets)
+                let result = dereplicate_partition(&dir, level, n_buckets);
+                pb.set_message(format!("last {:.0}ms", t.elapsed().as_millis()));
+                pb.inc(1);
+                result
             })
             .collect();
 
+        pb.finish_and_clear();
         for r in results {
             r?;
         }